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 BEIRUT, Lebanon — The leader of the Nusra Front, an affiliate of Al Qaeda in Syria, on Tuesday proposed an initiative aimed at halting the worst infighting yet between the armed opponents of President Bashar al-Assad since the start of the conflict nearly three years ago. 
 
 Deadly battles have raged in recent days across northern Syria between rebel forces and another Qaeda affiliate, known as the Islamic State of Iraq and Syria, or ISIS, that also wants to depose Mr. Assad’s government but aims to replace it with a monolithic Sunni extremist government that rules both countries. 
 
 Angered by what they call the tendency of the Islamic State of Iraq and Syria to commandeer resources, impose strict social codes, and kidnap and kill opponents, rebel groups have been attacking its bases and trying to drive out its fighters from towns and villages where they once held sway. 
 
 More than 270 people had been killed in four days of fighting as of Monday, according to the Syrian Observatory for Human Rights, an opposition group based in Britain with a network of contacts in Syria. The dead include 46 civilians, 129 rebel fighters and 99 fighters for the Islamic State of Iraq and Syria. Both sides have also executed prisoners, the Syrian Observatory said. 
 
 In an audio recording released online on Tuesday, the head of the Nusra Front, known as Abu Mohammed al-Jolani, said the infighting resulted from the “incorrect policies” of the Islamic State of Iraq and Syria. He called for a cease-fire and the establishment of an Islamic court to handle disputes, saying the violence could give Mr. Assad’s forces the opportunity to regain territory. 
 
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 “The whole battlefield, including the foreign and local fighters, will pay the price of losing a great jihad because the regime will rebound when it was so close to vanishing,” he said. 
 
 While rebel forces have in the past established Islamic courts to administer individual towns and villages, the movement has never had a unified leadership that could impose discipline. 
 
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 The authenticity of the Nusra Front leader’s statement could not be immediately confirmed. 
 
 The Syrian Observatory has reported that more than 130,000 people have been killed since the conflict began in March 2011. But the United Nations, which has been saying for months that the death toll has exceeded 100,000, announced on Tuesday that it had decided to stop updating its own tally, at least for the foreseeable future, because of the problems in verifying information. 
 
 “It was always very close to the edge in terms of how much we could guarantee the source material was accurate,” Rupert Colville, a spokesman for the United Nations high commissioner for human rights, told reporters in Geneva. He partly attributed the decision to the extremely limited ability of the United Nations to independently conduct fact-finding in Syria, making it “increasingly difficult for us to source and analyze the casualty figures in order to update them.” 
 
 Suspension of a United Nations update on casualties “will be a loss — we will now have only disparate sources of information,” said Hamit Dardagan, an author of a report on Syrian casualties by the Oxford Research Group, a London-based organization that put the toll at 113,700 as of November. 
 
 Mr. Dardagan, a founder of Iraq Body Count, a project begun in 2003 to record civilian casualties from the war in Iraq, also said the sectarian nature of the Syrian crisis would further complicate any data collection. “As any conflict intensifies and you have more refugee flows and more people displaced, that becomes more difficult,” he said in an interview. 
 
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 The number of nongovernmental organizations able to work in Syria has been reduced by the increasing violence. Civilian groups that report events considered unfavorable to any of the warring parties have been targeted; most recently, Razan Zeitouneh, a rights activist who ran the Violations Documentation Center, and her colleagues were abducted from their office in a Damascus suburb. Parties on both sides also actively filter information they provide to the outside world to help their cause, and government restrictions and the threat of kidnapping and death have severely limited access for journalists. 
 
 United Nations agencies that do have some access have also described problems in verifying data. Officials with the World Food Program and the World Health Organization in Damascus said recently that because their officials could not reach many areas in Syria, they had set up local contacts to relay information to them, but that verification was difficult. Government ministries provide some data, but they are out of touch with branches in some rebel-held areas. 
 
 The United Nations reported some progress on Tuesday in the international effort to purge Syria’s chemical weapons stockpile. In a statement issued with the Organization for the Prohibition of Chemical Weapons, it said the first batch of the most dangerous materials in the stockpile had been exported from the country, loaded onto a Danish commercial vessel in the Syrian port of Latakia. 
 
 The statement said the Danish vessel would remain at sea until the second cargo of chemicals reached Latakia, when it would return to load them. The vessel was escorted by Danish and Norwegian naval vessels, the statement said, and China and Russia were providing further maritime security for the operation. 
 
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 “This movement initiates the process of transfer of chemical materials from the Syrian Arab Republic to locations outside its territory for destruction,” said the statement by Sigrid Kaag, the United Nations official responsible for coordinating the effort. 
 
 The export and destruction of the most dangerous substances in the Syrian arsenal, which the statement called “priority chemical materials,” has long been considered the trickiest and most hazardous part of the operation, which Syria agreed to carry out as part of its pledge more than three months ago to renounce chemical weapons and join the treaty that bans them. 
 
 Under a Security Council resolution approved Sept. 27, all of Syria’s chemical weapons must be destroyed by the middle of 2014. The most dangerous chemicals were supposed to have been exported from the country by Dec. 31, but that stage of the operation was delayed because the war had made their overland transport to Latakia too dangerous to complete. ||||| Washington (CNN) Russian involvement in the 4½-year-old Syrian civil war seems to be escalating, with NATO's secretary general confirming Tuesday a second incursion by Russian planes into Turkish airspace and saying Russian ground troops were in Syria as well. 
 
 Damascus skies erupt with anti-aircraft fire as the US and its allies launch an attack on Syria's capital early on April 14, 2018. US President Donald Trump announced airstrikes in retaliation for Syria's alleged use of chemical weapons. Trump says the strikes are part of a sustained military response, in coordination with France and the United Kingdom. 
 
 Damascus skies erupt with anti-aircraft fire as the US and its allies launch an attack on Syria's capital early on April 14, 2018. US President Donald Trump announced airstrikes in retaliation for Syria's alleged use of chemical weapons. Trump says the strikes are part of a sustained military response, in coordination with France and the United Kingdom. 
 
 Bodies lie on the ground in the rebel-held city of Douma, Syria, on April 8, 2018. According to activist groups, helicopters dropped barrel bombs filled with toxic gas on Douma, which has been the focus of a renewed government offensive that launched in mid-February. The Syrian government and its key ally, Russia, vehemently denied involvement and accused rebel groups of fabricating the attack to hinder the army's advances and provoke international military intervention. 
 
 A child receives medical treatment after a village was attacked in the rebel-held Eastern Ghouta region on February 25, 2018. Several people were treated for exposure to chlorine gas, opposition groups said, as airstrikes and artillery fire from the regime continued. CNN was unable to independently verify claims that chlorine was used as a weapon. 
 
 A child receives medical treatment after a village was attacked in the rebel-held Eastern Ghouta region on February 25, 2018. Several people were treated for exposure to chlorine gas, opposition groups said, as airstrikes and artillery fire from the regime continued. CNN was unable to independently verify claims that chlorine was used as a weapon. 
 
 A member of the Syrian pro-regime forces fires a machine gun as a comrade holds his feeding ammunition belt on November 11, 2017. It was during an advance toward rebel-held positions west of Aleppo. 
 
 A member of the Syrian pro-regime forces fires a machine gun as a comrade holds his feeding ammunition belt on November 11, 2017. It was during an advance toward rebel-held positions west of Aleppo. 
 
 Residents of the war-torn city of Douma break their Ramadan fast on June 18, 2017. 
 
 Residents of the war-torn city of Douma break their Ramadan fast on June 18, 2017. 
 
 Members of the UN Security Council raise their hands on April 12, 2017, as they vote in favor of a draft resolution that condemned the reported use of chemical weapons in Syria. 
 
 Members of the UN Security Council raise their hands on April 12, 2017, as they vote in favor of a draft resolution that condemned the reported use of chemical weapons in Syria. 
 
 This photo, provided by the activist Idlib Media Center, shows dead children after a suspected chemical attack in the rebel-held city of Khan Sheikhoun on April 4, 2017. Dozens of people were killed, according to multiple activist groups. The United States responded a few days later by launching between 50-60 Tomahawk missiles at a Syrian government airbase. US officials said the base was home to warplanes that carried out the chemical attack. Syria has repeatedly denied it had anything to do with the attack. 
 
 This photo, provided by the activist Idlib Media Center, shows dead children after a suspected chemical attack in the rebel-held city of Khan Sheikhoun on April 4, 2017. Dozens of people were killed, according to multiple activist groups. The United States responded a few days later by launching between 50-60 Tomahawk missiles at a Syrian government airbase. US officials said the base was home to warplanes that carried out the chemical attack. Syria has repeatedly denied it had anything to do with the attack. 
 
 Arabic writing that reads "some day we will return" is seen on a bus window as civilians evacuate Aleppo on December 15, 2016. The evacuations began under a new ceasefire between rebels and pro-government forces. 
 
 Arabic writing that reads "some day we will return" is seen on a bus window as civilians evacuate Aleppo on December 15, 2016. The evacuations began under a new ceasefire between rebels and pro-government forces. 
 
 Smoke rises after an airstrike in Aleppo on October 4, 2016. 
 
 Smoke rises after an airstrike in Aleppo on October 4, 2016. 
 
 This still image, taken from a video posted by the Aleppo Media Center, shows a young boy in an ambulance after an airstrike in Aleppo, Syria, on August 17, 2016. It took nearly an hour to dig the boy, identified as Omran Daqneesh, out from the rubble, an activist told CNN. The airstrike destroyed his home, where he lived with his parents and two siblings. Director of the Aleppo Media Center Yousef Saddiq said Omran's 10-year-old brother, Ali, died from his injuries. 
 
 This still image, taken from a video posted by the Aleppo Media Center, shows a young boy in an ambulance after an airstrike in Aleppo, Syria, on August 17, 2016. It took nearly an hour to dig the boy, identified as Omran Daqneesh, out from the rubble, an activist told CNN. The airstrike destroyed his home, where he lived with his parents and two siblings. Director of the Aleppo Media Center Yousef Saddiq said Omran's 10-year-old brother, Ali, died from his injuries. 
 
 Members of a Syrian opposition group attack the headquarters of al-Assad regime forces in the Aleppo villages of Nubul and al-Zahraa on February 12, 2016. 
 
 Members of a Syrian opposition group attack the headquarters of al-Assad regime forces in the Aleppo villages of Nubul and al-Zahraa on February 12, 2016. 
 
 A sandstorm blows over damaged buildings in the rebel-held area of Douma, east of Damascus, on September 7, 2015. 
 
 A sandstorm blows over damaged buildings in the rebel-held area of Douma, east of Damascus, on September 7, 2015. 
 
 A refugee carries mattresses as he re-enters Syria from Turkey on June 22, 2015, after Kurdish People's Protection Units regained control of the area around Tal Abyad, Syria, from ISIS. 
 
 A refugee carries mattresses as he re-enters Syria from Turkey on June 22, 2015, after Kurdish People's Protection Units regained control of the area around Tal Abyad, Syria, from ISIS. 
 
 A Syrian child fleeing the war gets lifted over fences to enter Turkish territory illegally near a border crossing at Akcakale, Turkey, on June 14, 2015. 
 
 A Syrian child fleeing the war gets lifted over fences to enter Turkish territory illegally near a border crossing at Akcakale, Turkey, on June 14, 2015. 
 
 Nusra Front fighters inspect a helicopter belonging to pro-government forces after it crashed in the rebel-held Idlib countryside on March 22, 2015. 
 
 Nusra Front fighters inspect a helicopter belonging to pro-government forces after it crashed in the rebel-held Idlib countryside on March 22, 2015. 
 
 Rebel fighters dig caves in the mountains for bomb shelters in the northern countryside of Hama on March 9, 2015. 
 
 Rebel fighters dig caves in the mountains for bomb shelters in the northern countryside of Hama on March 9, 2015. 
 
 Medics tend to a man's injuries at a field hospital in Douma after airstrikes on September 20, 2014. 
 
 Medics tend to a man's injuries at a field hospital in Douma after airstrikes on September 20, 2014. 
 
 Volunteers remove a dead body from under debris after shelling in Aleppo on August 29, 2014. According to the Syrian Civil Defense, barrel bombs are now the greatest killer of civilians in many parts of Syria. The White Helmets are a humanitarian organization that tries to save lives and offer relief. 
 
 Volunteers remove a dead body from under debris after shelling in Aleppo on August 29, 2014. According to the Syrian Civil Defense, barrel bombs are now the greatest killer of civilians in many parts of Syria. The White Helmets are a humanitarian organization that tries to save lives and offer relief. 
 
 Photographs of victims of the Assad regime are displayed as a Syrian army defector known as "Caesar," center, appears in disguise to speak before the House Foreign Affairs Committee in Washington. The July 31, 2014, briefing was called "Assad's Killing Machine Exposed: Implications for U.S. Policy." Caesar, apparently a witness to the regime's brutality, smuggled more than 50,000 photographs depicting the torture and execution of more than 10,000 dissidents. CNN cannot independently confirm the authenticity of the photos, documents and testimony referenced in the report. 
 
 Photographs of victims of the Assad regime are displayed as a Syrian army defector known as "Caesar," center, appears in disguise to speak before the House Foreign Affairs Committee in Washington. The July 31, 2014, briefing was called "Assad's Killing Machine Exposed: Implications for U.S. Policy." Caesar, apparently a witness to the regime's brutality, smuggled more than 50,000 photographs depicting the torture and execution of more than 10,000 dissidents. CNN cannot independently confirm the authenticity of the photos, documents and testimony referenced in the report. 
 
 Rebel fighters execute two men on July 25, 2014, in Binnish, Syria. The men were reportedly charged by an Islamic religious court with detonating several car bombs. 
 
 Rebel fighters execute two men on July 25, 2014, in Binnish, Syria. The men were reportedly charged by an Islamic religious court with detonating several car bombs. 
 
 A giant poster of al-Assad is seen in Damascus on May 31, 2014, ahead of the country's presidential elections. He received 88.7% of the vote in the country's first election after the civil war broke out. 
 
 A giant poster of al-Assad is seen in Damascus on May 31, 2014, ahead of the country's presidential elections. He received 88.7% of the vote in the country's first election after the civil war broke out. 
 
 A US ship staff member wears personal protective equipment at a naval airbase in Rota, Spain, on April 10, 2014. A former container vessel was fitted out with at least $10 million of gear to let it take on about 560 metric tons of Syria's most dangerous chemical agents and sail them out to sea, officials said. 
 
 A US ship staff member wears personal protective equipment at a naval airbase in Rota, Spain, on April 10, 2014. A former container vessel was fitted out with at least $10 million of gear to let it take on about 560 metric tons of Syria's most dangerous chemical agents and sail them out to sea, officials said. 
 
 A man holds a baby who was rescued from rubble after an airstrike in Aleppo on February 14, 2014. 
 
 A man holds a baby who was rescued from rubble after an airstrike in Aleppo on February 14, 2014. 
 
 An injured man is helped following an airstrike in Aleppo's Maadi neighborhood on December 17, 2013. 
 
 An injured man is helped following an airstrike in Aleppo's Maadi neighborhood on December 17, 2013. 
 
 Syrian children wait as doctors perform medical checkups at a refugee center in Sofia, Bulgaria, on October 26, 2013. 
 
 Syrian children wait as doctors perform medical checkups at a refugee center in Sofia, Bulgaria, on October 26, 2013. 
 
 Residents run from a fire at a gasoline and oil shop in Aleppo's Bustan Al-Qasr neighborhood on October 20, 2013. Witnesses said the fire was caused by a bullet from a pro-government sniper. 
 
 Residents run from a fire at a gasoline and oil shop in Aleppo's Bustan Al-Qasr neighborhood on October 20, 2013. Witnesses said the fire was caused by a bullet from a pro-government sniper. 
 
 The UN Security Council passes a resolution September 27, 2013, requiring Syria to eliminate its arsenal of chemical weapons. Al-Assad said he would abide by the resolution. 
 
 The UN Security Council passes a resolution September 27, 2013, requiring Syria to eliminate its arsenal of chemical weapons. Al-Assad said he would abide by the resolution. 
 
 An aerial view shows the Zaatari refugee camp near the Jordanian city of Mafraq on July 18, 2013. 
 
 An aerial view shows the Zaatari refugee camp near the Jordanian city of Mafraq on July 18, 2013. 
 
 Rebels launch a missile near the Abu Baker brigade in Al-Bab, Syria, on January 16, 2013. 
 
 Rebels launch a missile near the Abu Baker brigade in Al-Bab, Syria, on January 16, 2013. 
 
 Syrians look for survivors amid the rubble of a building targeted by a missile in the al-Mashhad neighborhood of Aleppo on January 7, 2013. 
 
 Syrians look for survivors amid the rubble of a building targeted by a missile in the al-Mashhad neighborhood of Aleppo on January 7, 2013. 
 
 A father reacts after the deaths of two of his children in Aleppo on January 3, 2013. 
 
 A father reacts after the deaths of two of his children in Aleppo on January 3, 2013. 
 
 The bodies of three children are laid out for identification by family members at a makeshift hospital in Aleppo on December 2, 2012. The children were allegedly killed in a mortar shell attack that landed close to a bakery in the city. 
 
 The bodies of three children are laid out for identification by family members at a makeshift hospital in Aleppo on December 2, 2012. The children were allegedly killed in a mortar shell attack that landed close to a bakery in the city. 
 
 Smoke rises in the Hanano and Bustan al-Basha districts in Aleppo as fighting continues through the night on December 1, 2012. 
 
 Smoke rises in the Hanano and Bustan al-Basha districts in Aleppo as fighting continues through the night on December 1, 2012. 
 
 An Israeli tank crew sits on the Golan Heights overlooking the Syrian village of Breqa on November 6, 2012. Israel fired warning shots toward Syria after a mortar shell hit an Israeli military post. It was the first time Israel fired on Syria across the Golan Heights since the 1973 Yom Kippur War. 
 
 An Israeli tank crew sits on the Golan Heights overlooking the Syrian village of Breqa on November 6, 2012. Israel fired warning shots toward Syria after a mortar shell hit an Israeli military post. It was the first time Israel fired on Syria across the Golan Heights since the 1973 Yom Kippur War. 
 
 A Syrian rebel walks inside a burnt section of the Umayyad Mosque in Aleppo hours before the Syrian army retook control of the complex on October 14, 2012. 
 
 A Syrian rebel walks inside a burnt section of the Umayyad Mosque in Aleppo hours before the Syrian army retook control of the complex on October 14, 2012. 
 
 Smoke rises over the streets after a mortar bomb from Syria landed in the Turkish border village of Akcakale on October 3, 2012. Five people were killed. In response, Turkey fired on Syrian targets and its parliament authorized a resolution giving the government permission to deploy soldiers to foreign countries. 
 
 Smoke rises over the streets after a mortar bomb from Syria landed in the Turkish border village of Akcakale on October 3, 2012. Five people were killed. In response, Turkey fired on Syrian targets and its parliament authorized a resolution giving the government permission to deploy soldiers to foreign countries. 
 
 Free Syrian Army fighters are reflected in a mirror they use to see a Syrian Army post only 50 meters away in Aleppo on September 16, 2012. 
 
 Free Syrian Army fighters are reflected in a mirror they use to see a Syrian Army post only 50 meters away in Aleppo on September 16, 2012. 
 
 A Syrian man carrying grocery bags dodges sniper fire in Aleppo as he runs through an alley near a checkpoint manned by the Free Syrian Army on September 14, 2012. 
 
 A Syrian man carrying grocery bags dodges sniper fire in Aleppo as he runs through an alley near a checkpoint manned by the Free Syrian Army on September 14, 2012. 
 
 Family members mourn the deaths of their relatives in front of a field hospital in Aleppo on August 21, 2012. 
 
 Family members mourn the deaths of their relatives in front of a field hospital in Aleppo on August 21, 2012. 
 
 A Free Syrian Army fighter runs for cover as a Syrian Army tank shell hits a building across the street during clashes in the Salaheddine neighborhood of central Aleppo on August 17, 2012. 
 
 A Free Syrian Army fighter runs for cover as a Syrian Army tank shell hits a building across the street during clashes in the Salaheddine neighborhood of central Aleppo on August 17, 2012. 
 
 Rebel fighters with the Free Syrian Army capture a police officer in Aleppo, Syria, who they believed to be pro-regime militiaman on July 31, 2012. Dozens of officers were reportedly killed as rebels seized police stations in the city. 
 
 Rebel fighters with the Free Syrian Army capture a police officer in Aleppo, Syria, who they believed to be pro-regime militiaman on July 31, 2012. Dozens of officers were reportedly killed as rebels seized police stations in the city. 
 
 Syrian refugees walk across a field in Syria before crossing into Turkey on March 14, 2012. 
 
 Syrian refugees walk across a field in Syria before crossing into Turkey on March 14, 2012. 
 
 Supporters of al-Assad celebrate during a referendum vote in Damascus on February 26, 2012. Opposition activists reported at least 55 deaths across the country as Syrians headed to the polls. Analysts and protesters widely described the constitutional referendum as a farce. "Essentially, what (al-Assad's) done here is put a piece of paper that he controls to a vote that he controls so that he can try and maintain control," a US State Department spokeswoman said. 
 
 Supporters of al-Assad celebrate during a referendum vote in Damascus on February 26, 2012. Opposition activists reported at least 55 deaths across the country as Syrians headed to the polls. Analysts and protesters widely described the constitutional referendum as a farce. "Essentially, what (al-Assad's) done here is put a piece of paper that he controls to a vote that he controls so that he can try and maintain control," a US State Department spokeswoman said. 
 
 Delegates from Arab League member states and Turkey discuss a response to the government's crackdown in Syria on November 16, 2011. 
 
 Delegates from Arab League member states and Turkey discuss a response to the government's crackdown in Syria on November 16, 2011. 
 
 Jamal al-Wadi speaks in Istanbul on September 15, 2011, after an alignment of Syrian opposition leaders announced the creation of a Syrian National Council -- their bid to present a united front against Bashar al-Assad's regime and establish a democratic system. 
 
 Jamal al-Wadi speaks in Istanbul on September 15, 2011, after an alignment of Syrian opposition leaders announced the creation of a Syrian National Council -- their bid to present a united front against Bashar al-Assad's regime and establish a democratic system. 
 
 Syrian children walk over bricks stored for road repairs during a spontaneous protest June 15, 2011, at a refugee camp near the Syrian border in Yayladagi, Turkey. 
 
 Syrian children walk over bricks stored for road repairs during a spontaneous protest June 15, 2011, at a refugee camp near the Syrian border in Yayladagi, Turkey. 
 
 Anti-government protesters demonstrate in Daraa on March 23, 2011. In response to continuing protests, the Syrian government announced several plans to appease citizens. 
 
 Anti-government protesters demonstrate in Daraa on March 23, 2011. In response to continuing protests, the Syrian government announced several plans to appease citizens. 
 
 An injured man lying in the back of a vehicle is rushed to a hospital in Daraa, Syria, on March 23, 2011. Violence flared in Daraa after a group of teens and children were arrested for writing political graffiti. Dozens of people were killed when security forces cracked down on demonstrations. 
 
 An injured man lying in the back of a vehicle is rushed to a hospital in Daraa, Syria, on March 23, 2011. Violence flared in Daraa after a group of teens and children were arrested for writing political graffiti. Dozens of people were killed when security forces cracked down on demonstrations. 
 
 Displaced Syrian residents wait to receive food aid distributed by the UN Relief and Works Agency at the besieged al-Yarmouk camp, south of Damascus, Syria, on January 31, 2014. According to the UN Envoy for Syria, an estimated 400,000 Syrians have been killed since an uprising in March 2011 spiraled into civil war. See how the conflict has unfolded. 
 
 Displaced Syrian residents wait to receive food aid distributed by the UN Relief and Works Agency at the besieged al-Yarmouk camp, south of Damascus, Syria, on January 31, 2014. According to the UN Envoy for Syria, an estimated 400,000 Syrians have been killed since an uprising in March 2011 spiraled into civil war. See how the conflict has unfolded. 
 
 "It's unacceptable, it's dangerous, and it's reckless behavior and it adds to the tensions," Secretary General Jens Stoltenberg told CNN about the incursions into Turkish airspace. 
 
 "We see the violation of the Turkish airspace becomes more important, more dangerous, because it happens in a context where we see more fighting, more Russian military presence in Syria." 
 
 Stoltenberg expressed alarm over how the Russian military grows on several fronts in Syria. 
 
 "So we have seen a substantial military buildup by Russia in Syria, both in the air with the combat planes and air defense systems, but also an increasing number of ground troops," he said. "In addition to that, they have deployed naval assets, a large number of naval assets close to the Syrian shores. And they continue to do so." 
 
 Alleged airspace violations 
 
 The first violation of Turkey's airspace is reported to have happened Saturday. The second was Sunday, officials said. 
 
 Turkey's President Recep Tayyip Erdogan had a warning for Moscow, according to the nation's semiofficial news agency, Anadolu. 
 
 "If Russia loses a friend like Turkey, with which it has conducted many businesses, it will lose a lot," he said. 
 
 NATO chief Jens Stoltenberg condemns Russia's incursion into Turkish airspace. 
 
 In addition to the incursion reports, the Turkish air force said a MiG-29 fighter jet of an unidentified nationality had interfered Monday with eight Turkish F-16s on the Turkey-Syria border. The Turkish air force reported the jet put its planes under a radar lock for four minutes and 30 seconds. 
 
 Stoltenberg rebuked Russian combat aircraft for two alleged violations of Turkey's airspace. 
 
 "We also have seen two of them, two violations of Turkish airspace," he said at a news conference. "Intelligence that we have received provides me with reason to say it doesn't look like an accident." 
 
 Turkey has been a member of NATO since 1952, and alliance rules say that an attack on any of the 28 member states should be treated as an attack on all. 
 
 Stoltenberg said the "substantial buildup of Russian forces in Syria" includes "ground troops in connection with the air base they have." 
 
 Stoltenberg said he doubted that Russia, which has been conducting airstrikes in Syria, was interested primarily in fighting the terrorist group ISIS, also known as ISIL. 
 
 "I'm also concerned that Russia is not targeting ISIL but instead attacking the Syrian opposition and civilians," he said. 
 
 U.S.: Russia moved weapons, troops into Syria 
 
 The Pentagon also is worried about Russia's military activity in Syria. 
 
 The latest U.S. assessment indicates that Russia has moved ground combat weapons and troops to operate them into areas of western Syria where anti-regime forces are, according to two American defense officials. The United States sees the move as Russia "stepping up its ground activity" in Syria to attack those forces, rather than ISIS elements, according to one of the officials. 
 
 But Russian officials deny ramping up military activity. Officials quoted by state media said there would be no ground operation in Syria and -- in contrast to what officials had said earlier -- Russia would try to prevent any "volunteers" from going to Syria. 
 
 The tension between Russia and Turkey, however, appears to be escalating. The two countries are at odds over the civil war in Syria, with Russia backing Syrian President Bashar al-Assad. 
 
 "I discussed the situation in Syria with Foreign Minister Lavrov in New York last week," Stoltenberg said, referring to Russian Foreign Minister Sergey Lavrov. "I urge Russia to play a constructive and cooperative role in the fight against ISIL. And to strive for a negotiated political solution to the conflict in Syria." 
 
 Conflicting reports on strikes in Syria 
 
 As diplomats talked, the violence in Syria continued unabated. 
 
 Syrian state media reported that joint Russian and Syrian airstrikes had hit ISIS targets in the modern city of Palmyra, adjacent to its ancient ruins. The airstrikes hit "ISIS hideouts," destroying 20 armored vehicles, three ammunition dumps as well as rocket launch pads, the SANA news agency reported, citing unnamed military sources. 
 
 The London-based Syrian Observatory for Human Rights reported that Russian strikes in and around Palmyra killed at least 15 ISIS militants and destroyed vehicles, posts and ammunition dumps there. Four more members of the terrorist group died in strikes in Raqqa, the Syrian city that has been referred to as ISIS' de facto capital. 
 
 But Russian state media denied the Palmyra strikes. 
 
 "All foreign media reports suggesting that Russian planes have allegedly launched airstrikes on the city of Palmyra are totally untrue," Defense Ministry spokesman Maj. Gen. Igor Konashenkov said, according to Tass 
 
 "We don't rule out that terrorists may be preparing provocations in this and other settlements — to blast mosques and then demonstrate fake photo and video materials with accusations against Russian aircraft on the territory of the Syrian Arab Republic," the general said in the Tass report. 
 
 However, another Russian state news agency, RIA Novosti, reported that Russian jets hit ISIS targets 28 kilometers (about 17 miles) from Palmyra. 
 
 Obama authorizes resupply of opposition 
 
 On Monday, U.S. President Barack Obama authorized the resupply of Syrian Kurds and the Arab-Syrian opposition as part of a strategy to put pressure on ISIS from the north and strengthen the border, according to two senior administration officials. 
 
 The approval came at a National Security Council meeting Thursday. 
 
 CNN reported over the weekend that Obama emphasized to his team that the United States would continue to support the Syrian opposition as Russia enters the war-torn country. 
 
 "President Obama was clear that we intend to continue our efforts to degrade and ultimately destroy ISIL in Syria and to keep supporting the moderate Syrian opposition," an official said. 
 
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 Russia's aims questioned 
 
 Russia has said it is conducting military operations to wipe out ISIS and other extremist groups. U.S. officials have seen the effort primarily as a move to bolster al-Assad, a close ally -- a goal Russian President Vladimir Putin does not deny. 
 
 It's believed the Russians are positioning weapons to support a Syrian ground offensive, officials said. 
 
 The equipment includes artillery as well as four BM-30 multiple-launch rocket systems -- all considered to be highly accurate. The latter is capable of rapid-fire rocket launches. 
 
 Officials: Russia brings electronic jamming equipment 
 
 Several weeks ago, Russia moved about half a dozen artillery pieces into the port of Latakia. 
 
 The United States originally thought the move might be for defense of the port, but the latest action is an indication of potential ground attacks in the coming days, an official said. 
 
 The weapons have been spotted between Homs and Idlib and west of Idlib. 
 
 It is not clear if they're now in final position for possible artillery strikes. 
 
 The officials also said Russia has moved electronic jamming equipment into Syria. Both a truck-mounted system and a number of pods that can go on aircraft have been observed. The equipment could potentially give the Russians the ability to jam electronics of U.S-backed coalition aircraft. ||||| Media playback is unsupported on your device Media caption The BBC's Jim Muir meets the Syrian children who do not officially exist 
 
 UN agencies say the number of children forced to flee Syria has reached one million, describing the figure as "a shameful milestone". 
 
 The UN's refugee agency and Unicef say a further two million children are displaced within the country. 
 
 More than 100,000 people have been killed in the conflict, according to UN Secretary General Ban Ki-moon. 
 
 He has also called for an investigation "without delay" into the recent alleged chemical weapons attack near Damascus. 
 
 Activists say hundreds were killed in Wednesday's attack, and Mr Ban is sending disarmament chief Angela Kane to Damascus to press for an investigation, his spokesman Eduardo del Buey said on Thursday. 
 
 Russia - Syrian President Bashar al-Assad's main ally - on Friday urged Syrian rebels to ensure that a UN team already in the country had safe access to the site of the alleged attack. 
 
 'Traumatised' 
 
 The UN says children now make up half of all refugees fleeing Syria. About three-quarters of those children are under 11. 
 
 "The youth of Syria are losing their homes, their family members and their futures," said UN high commissioner for refugees Antonio Guterres. 
 
 "Even after they have crossed a border to safety, they are traumatised, depressed and in need of a reason for hope," he said. 
 
 Most of the children have arrived in Lebanon, Jordan, Turkey, Iraq and Egypt, the UN says, and increasingly Syrians are fleeing to North Africa and Europe. 
 
 But with its appeal for Syria less than 40% funded, the two UN agencies say they are struggling to meet the needs of the refugees. 
 
 Just 118,000 of the refugee children have been able to continue in some sort of education, and a fifth have received psychosocial counselling. 
 
 The BBC's Imogen Foulkes in Geneva says the agencies are now warning of a lost generation that are ill-equipped to bring peace and stability to their country in the future. 
 
 "We must all share the shame," said Unicef executive director Anthony Lake, "because while we work to alleviate the suffering of those affected by this crisis, the global community has failed in its responsibility to this child. 
 
 "We should stop and ask ourselves how, in all conscience, we can continue to fail the children of Syria." 
 
 Roger Hearn, Save the Children's regional director for the Middle East, added: "It is appalling that the world has stood and watched as one million children have been forced from their country, terrified, traumatised and in some cases orphaned." 
 
 The UN says the conflict in Syria has caused the world's worst refugee crisis for 20 years, with numbers not seen since the 1994 genocide in Rwanda. 
 
 Media playback is unsupported on your device Media caption Syrian refugees have also swamped the border crossing into Iraqi Kurdistan, Jim Muir reports 
 
 It says more than 1.7million people have registered as refugees since the uprising against the rule of President Assad began in March 2011. 
 
 More than 40,000 Syrians have poured over the border of Iraqi Kurdistan since a new wave of arrivals began in the region a week ago. 
 
 Shocking footage 
 
 Speaking of the alleged chemical attack, Mr Ban said: "Any use of chemical weapons anywhere, by anybody, under any circumstances, would violate international law. Such a crime against humanity should result in serious consequences for the perpetrator." 
 
 Mr Ban has asked the Syrian government to let UN weapons inspectors, who are already in the country, investigate the allegations. 
 
 Media playback is unsupported on your device Media caption UN Secretary-General Ban Ki-moon: "Chemical weapons... would violate international law" 
 
 "I can think of no good reason why any party - either government or opposition forces - would decline this opportunity to get to the truth of the matter," Mr Ban said from the South Korean capital, Seoul. 
 
 The inspection team currently only has a mandate to visit three previously agreed sites, including the northern town of Khan al-Assal, where some 26 people were killed in an alleged chemical attack in March. 
 
 There is no sign yet that Damascus will allow the team to extend its mission, and Syrian adviser Bassam Abu Abdullah told the BBC he believed it would not be allowed to visit the site. 
 
 Dr Bassam said the chemical attack was carried out by what he called a terrorist group, to prevent a military operation by the Syrian army. 
 
 The government earlier described the allegations that it sanctioned the use of chemical weapons as "illogical and fabricated". 
 
 But unverified footage shows civilians - many of them children - apparently suffering horrific symptoms, as well as rows of shrouded bodies. 
 
 Chemical weapons experts have told the BBC that footage appears genuine and that the injuries shown are consistent with nerve agents. 
 
 International clamour over the alleged chemical attacks has continued to grow. 
 
 French Foreign Minister Laurent Fabius warned that France must react "with force" if the use of chemical weapons was confirmed. 
 
 The US state department said it was urgently gathering information to try to determine what had taken place in Damascus.
– The horrific toll civil war is taking on the children of Syria is laid bare in the first major report to focus on the issue. At least 11,420 children, more than a tenth of the conflict's casualties, have been killed since the conflict began in March 2011, including hundreds who were shot dead by snipers or summarily executed, the report from a London think-tank finds. Teenage boys were the most likely to be killed but children as young as just a year old have been tortured and executed, reports the BBC. Bombing and shelling were the cause of most deaths and the report's authors have urged both sides to stop targeting civilians. More than 2.1 million refugees have now fled the conflict and the United Nations, which says this is the worst refugee crisis in a generation, warns that there could be 3.5 million refugees by the end of the year, reports the New York Times. To make matters even worse for internally displaced Syrians, al-Qaeda fighters have been making major gains in northern Syria in recent months, displacing more moderate opposition groups and imposing strict Islamic law in areas under their control, CNN finds. The jihadist groups are even more dangerous in Syria than they were in Iraq, and are "more likely to sustainably control territory, project power around the region, possibly sponsor global terrorist attacks, and catalyze a new generation of jihadist insurrection," a counterterrorism expert warns.