Story highlights The Iraqi air force killed more than 200 ISIS militants, according to Iraq state TV 
 
 U.S. may try to speak directly to Iran about deteriorating Iraq situation, senior U.S. officials say 
 
 Dozens of U.S. military personnel arrive at U.S. Embassy, a U.S. official says 
 
 Photos appearing online appear to show ISIS fighters executing Iraqi security forces 
 
 The Iraqi air force struck back at the militant group ISIS , the Islamic State in Iraq and Syria, killing more than 200 militants, Iraqi state TV reported Monday morning. The air raids took place in Saqlawiyah, northwest of Fallujah, according to a graphic run by state TV. 
 
 ISIS has been ruthlessly fighting to take control of Iraq and has apparently posted chilling photos on jihadi Internet forums seeming to show the executions of Iraqi security forces. 
 
 CNN cannot independently confirm the authenticity of the images purportedly posted by ISIS . CNN is examining the terrain in the images, some of the signage on buildings in several of the pictures and the uniforms of the apparent victims. Those details suggest the photos are real and were taken in Iraq. 
 
 A caption on some of the images reads: "apostates heading to their hole of doom." 
 
 ISIS, an al Qaeda splinter group, wants to establish a caliphate, or Islamic state, that would stretch from Iraq into northern Syria. The group has had substantial success in Syria battling Syrian President Bashar al-Assad's security forces. 
 
 On Friday, a tweet on what was claimed to be an ISIS Twitter account claimed that its members killed at least 1,700 Shiites. CNN was unable to verify the authenticity of the account, and the account appeared to have been taken down Sunday. 
 
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 In a statement, the U.S. State Department condemned the claim by ISIS, also known as ISIL, the Islamic State of Iraq and the Levant. 
 
 "The claim by the Islamic State of Iraq and the Levant (ISIL) that it has massacred 1700 Iraqi Shia air force recruits in Tikrit is horrifying and a true depiction of the bloodlust that these terrorists represent. While we cannot confirm these reports, one of the primary goals of ISIL is to set fear into the hearts of all Iraqis and drive sectarian division among its people," part of the statement read. "Terrorists who can commit such heinous acts are a shared enemy of the United States, Iraq, and the international community. " 
 
 The militants' quick advance in Iraq has been helped by many Sunnis who feel that the Shiite-dominated government has marginalized them. 
 
 ISIS seized Iraq's second-largest city, Mosul, last week and has threatened to march on Baghdad, Iraq's capital and largest city. 
 
 But "Mosul didn't fall," a defiant Iraqi Prime Minister Nuri al-Maliki told military leaders in Baghdad in a speech televised Sunday on state TV. "The ones who have fallen are the politicians who have bet against Iraq." The Prime Minister said, "We will not allow anyone to divide the Iraqi people." 
 
 Al-Maliki called on his top brass and soldiers to march and fight against ISIS, while criticizing Iraqi politicians conspiring against their homeland and Iraqi soldiers who have refused to continue to fight when confronted by ISIS. 
 
 "We will march on every inch, with all our weapons, with all our will and faith, so we can liberate and cleanse every inch of Iraq -- from the southernmost point to the furthest point in the north," he exhorted the military leaders. 
 
 Despite al-Maliki's bold statements, ISIS accumulated several victories across Iraq on Sunday. 
 
 The northwest Iraqi city of Tal Afar fell to ISIS, according to Iraqi Gen. Mohammed al-Quraishi. Many Tal Afar residents -- ethnic minority Shiite Turkmen -- fled the fighting north toward Iraq's Kurdish region. Tal Afar is in Nineveh province, midway between the country's border with Syria and Mosul, north of Baghdad. 
 
 Before Iraqi security forces lost Tal Afar, several mortar rounds landed on a busy area in the town and killed at least seven and wounded 33 people, security officials in Baghdad and Tal Afar told CNN. 
 
 Also Sunday, ISIS gained control of two villages in Adhaim, in its first push into Diyala province, northeast of Baghdad. 
 
 On top of that, Iraqi security forces and gunmen believed to be ISIS clashed near al-Khalis, about 18 miles from Diyala's capital, Baquba, al-Khalis police officials told CNN. Three mortar rounds landed near a recruitment center opened recently for volunteers to help the Iraqi army fight against ISIS. 
 
 Baquba is about 37 miles northeast of Baghdad. Baquba is an ethnically-mixed city, though Sunnis represent a slight majority. 
 
 Given Baquba's proximity to Baghdad, if Baquba were to fall, it could give ISIS militants three-pronged access to Baghdad -- from Anbar province to the west, Ninevah and Salahuddin provinces to the north and from Diyala province from the northeast. 
 
 Meanwhile, on Sunday, CNN Senior International Correspondent Arwa Damon was in the Iraqi Kurdish province of Kirkuk, where last Thursday militants took control of two villages. 
 
 She asked the local governor, Dr. Najmaldin Karim, whether the United States should launch airstrikes to help fight back ISIS. 
 
 "I think they know how to do it, but blanket bombing is not going to work here," Karim said, explaining that that approach ignores the fact that ISIS is too blended into the civilian population in Kirkuk and innocent people could die. But there should be targeted bombing in both Iraq and Syria, he said. 
 
 "I don't think anyone is safe from these people," said Karim. 
 
 Partial staff relocation at U.S. Embassy 
 
 Between 50 and 100 U.S. Marines and U.S. Army personnel have arrived at the U.S. Embassy in Baghdad, a U.S. official told CNN on Sunday. 
 
 A U.S official acknowledged to CNN that the additional embassy security personnel being added include U.S. Marines who specialize in embassy protection during high-threat conditions. 
 
 The U.S. invaded Iraq in 2003. American military forces ended their withdrawal from the country in December 2011. 
 
 At the time of the U.S. drawdown, Iraq's leadership had agreed that a residual U.S. military presence was desirable, but the talks broke down over the prickly issue of legal immunity for U.S. troops in Iraq. 
 
 The Obama administration had said any deal to keep U.S. troops in Iraq beyond the withdrawal deadline would require a guarantee of legal protection for American soldiers. But the Iraqis refused to agree to that, opening up the prospect of American troops being tried in Iraqi courts and subjected to Iraqi punishment. 
 
 This week, President Barack Obama continued to consider options with regard to the situation in Iraq but ruled out sending troops into the country. 
 
 On Sunday, U.S. State Department spokeswoman Jen Psaki said that some U.S. security personnel will be added to the staff at the U.S. Embassy in Baghdad and other staff members will be temporarily relocated to consular offices in Basra and Irbil and to the Iraq Support Unit in Amman, Jordan. 
 
 A "substantial majority of the U.S. Embassy presence in Iraq will remain in place," Psaki said in a statement, and "the Embassy will be fully equipped to carry out its national security mission." 
 
 Pentagon Press Secretary Rear Adm. John Kirby said that a "small number of Defense Department personnel" are augmenting State Department security assets in Baghdad. Kirby said that the relocation of some embassy personnel is being done with commercial, charter and State Department aircraft flights. 
 
 The U.S. military can airlift people if the State Department asks for that, Kirby said. 
 
 The State Department is warning U.S. citizens against "all but essential travel to Iraq." The official travel warning says U.S. citizens in Iraq "remain at high risk for kidnapping and terrorist violence." 
 
 While that continues, Iran has recently entered the fray, according to a senior security official in Baghdad who spoke to CNN on Friday. That official said that in recent days, Iran has sent about 500 Iranian Revolutionary Guard troops to fight alongside Iraqi government security forces in Iraq's Diyala province. 
 
 However, Iranian officials, including President Hassan Rouhani , denied reports that some of its elite forces are in Iraq to help bolster al-Maliki, a fellow Shiite. 
 
 "If the Iraqi government wants us to help, we will consider it," Rouhani said, according to an English translation of his remarks Saturday in Farsi by state-run Press TV. 
 
 But, he said, "so far they have not asked specifically for help," and added that Iran could give strategic guidance if requested. 
 
 The Obama administration is exploring possible direct talks with Iran over the deteriorating situation in Iraq, two senior U.S. officials tell CNN. 
 
 Both officials ruled out any type of teaming up with Iran because the United States and Iran don't have a lot of common interests -- other than a stable Iraq. 
 
 The United States is wary of furthering Iran's already considerable influence in Iraq. The Shiite Iranian regime is al-Malaki's closest ally in the region. Additionally the administration is concerned appearing to team up with Iran would both alienate Iraq's Sunni majority and worry Sunni allies of the United States in the region. 
 
 The State Department statement said the United States "will do its part to help Iraq move beyond this crisis," and a senior State Department officer told CNN that Kerry spoke to his counterparts from Jordan, the UAE, Saudi Arabia and Qatar to discuss the threat posed by ISIS. 
 
 The administration has not yet determined what the mechanism would be for talking to Iran, the senior U.S. officials said. 
 
 Ex-U.S. ambassador: Kerry should go to Iraq 
 
 On Sunday U.S. Sen. Lindsey Graham argued on CNN's "State of the Union" for more intervention in Iraq. 
 
 The South Carolina Republican, a frequent critic of the Obama administration's approach to foreign policy, called Obama "stubborn-headed," "delusional" and "detached" over his decision on how to react to the unfolding crisis. 
 
 "Time is running out to turn this around," Graham said. "Get involved with air power. Stop the march toward Baghdad. Deal with Syria. But get a new government (in Iraq) in place as quickly as you can that will bring the Iraqis back together for a counteroffensive." 
 
 Ryan Crocker, the U.S. ambassador to Iraq from 2007 to 2009, told CNN's Fareed Zakaria on Sunday that he thinks Secretary of State John Kerry should fly to Iraq immediately. 
 
 "We need the secretary of state out there in Baghdad right now," Crocker said. "We need the President on the phone to the Iraqi leadership because the reality is the Iraqis are not in a position ... they were not in a position when I was there, they are not in a position now, to work out hard compromises on their own." 
 
 The United States is the "middleman among Sunni, Shia and Kurds," Crocker said. "Ambassadors can go just so far." 
 
 Crocker, now the dean of the George Bush School of Government & Public Service at Texas A&M University, said he would support "very carefully targeted airstrikes" in conjuction with high-level diplomacy. 
 
 "We have got to help the Iraqis come together," Crocker urged, "in a unified fashion to confront a common threat." ||||| Photo Advertisement Continue reading the main story 
 
 BAGHDAD — Wielding the threat of sectarian slaughter, Sunni Islamist militants claimed on Sunday that they had massacred hundreds of captive Shiite members of Iraq’s security forces, posting grisly pictures of a mass execution in Tikrit as evidence and warning of more killing to come. 
 
 
 
 
 
 
 
 
 
 The possible mass killing came as militants cemented control of the city of Tal Afar, west of Mosul, after two days of fierce clashes with Iraqi troops, residents and senior security officials said. The city came under mortar attack, sending many residents fleeing toward Sinjar to the west and Mosul to the east. Residents said the militants freed dozens of prisoners. 
 
 Even as anecdotal reports of extrajudicial killings around the country seemed to bear out the Islamic State in Iraq and Syria’s intent to kill Shiites wherever it could, Iraqi officials and some human rights groups cautioned that the militants’ claim to have killed 1,700 soldiers in Tikrit could not be immediately verified. 
 
 But with their claim, the Sunni militants were reveling in an atrocity that if confirmed would be the worst yet in the conflicts that roil the region, outstripping even the poison gas attack near Damascus last year. 
 
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 In an atmosphere where there were already fears that the militants’ sudden advance near the capital would prompt Shiite reprisal attacks against Sunni Arab civilians, the claims by ISIS were potentially explosive. And that is exactly the group’s stated intent: to stoke a return to all-out sectarian warfare that would bolster its attempts to carve out a Sunni Islamist caliphate that crosses borders through the region. 
 
 The sectarian element of the killings may put more pressure on the Obama administration to aid Iraq militarily. In fact, the militants seemed to be counting on it. A pronouncement on Sunday by the group’s leader, Abu Bakr al-Baghdadi, had a clear message for the United States: “Soon we will face you, and we are waiting for this day.” 
 
 The group’s announcement was made in a series of gruesome photographs uploaded to an ISIS Twitter feed and on websites late on Saturday night. Some showed insurgents, many wearing black masks, lining up at the edges of what looked like shallow mass graves and apparently firing their weapons into young men who had their hands bound behind their backs and were packed closely together in large groups. 
 
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 The photographs showed what appeared to be seven massacre sites, although several of them may have been different views of the same sites. In any one of the pictures, no more than about 60 victims could be seen and sometimes as few as 20 at each of the sites, although it was not clear if the photographs showed the entire graves. 
 
 The militants’ captions seemed tailor-made to ignite anger and fear among Shiites. “The filthy Shiites are killed in the hundreds,” one read. “The liquidation of the Shiites who ran away from their military bases,” read another, and, “This is the destiny of Maliki’s Shiites,” referring to Prime Minister Nuri Kamal al-Maliki. 
 
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 Many of the captions mocked the victims. In one photograph, showing a group of young men walking toward an apparent execution site, where armed masked men awaited, the caption read, “Look at them walking to death on their own feet.” 
 
 So far, Iraq’s majority Shiites were not rising to the bait. Grand Ayatollah Ali al-Sistani, their supreme religious leader, issued a statement on Saturday calling for all groups to “exert the highest possible level of self-restraint during this tumultuous period.” And there was little immediate public reaction to the ISIS claims in Baghdad or other southern Iraqi cities. 
 
 A senior Iraqi government official, speaking on the condition of anonymity because he was not authorized to make press statements, said news of the executions was slow to circulate because Twitter and other social media sites had been blocked for days. “I don’t doubt they are real, but 1,700 is a big number,” he said. “We are trying to control the reaction.” 
 
 Acutely aware of the potential for retaliatory violence, some government officials who had heard about the ISIS claims took pains to play them down, confirming only that some executions had taken place in Tikrit, but not on a large scale. 
 
 One Iraqi security official claimed that no more than 11 bodies of executed soldiers were recovered from the Tigris River downstream from the execution site, a group of six and a group of five, although he confirmed that 800 soldiers had been taken prisoner in the area. He also reported finding 17 bodies washed up against a dam near Samarra, another city the militants are fighting for. But he said, “There is no such superstitious number as 1,700 people executed.” 
 
 An official statement posted on the Ministry of Defense’s website denied the executions had taken place at all. 
 
 Still, other officials and human rights representatives, while cautioning that they could not confirm the full 1,700 number being claimed, said that ISIS had shown no compunctions against hunting Shiites. And they reiterated that such horrific claims would go to further the group’s intent to sow chaos. 
 
 “We’re trying to verify the pics, and I am not convinced they are authentic,” said Erin Evers, the Human Rights Watch researcher in Iraq. “As far as ISIS claiming it has killed 1,700 people and publishing horrific photos to support that claim, it is unfortunately in keeping with their pattern of commission of atrocities, and obviously intended to further fuel sectarian war.” 
 
 Col. Suhail al-Samaraie, head of the Awakening Council in Samarra, a pro-government Sunni grouping, confirmed that officials in Salahuddin Province were aware that large-scale executions had taken place, but did not know how many. “They are targeting anyone working with the government side, any place, anywhere,” he said. He said the insurgents were targeting both Sunnis and Shiites, anyone with a government affiliation, but claiming for propaganda reasons that the victims were all Shiites. 
 
 A New York Times employee in Tikrit said local residents saw hundreds of Iraqi military personnel captured when they tried to flee Camp Speicher, a former American military base and airfield now used as an air force training center on the edge of Tikrit. It is still in government hands. 
 
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 Most of those captured were air force cadets, the employee said. Those who were Sunnis were given civilian clothes and sent home; the Shiites were marched and trucked off to the grounds of Saddam Hussein’s old palace in Tikrit, where they reportedly were executed. He added that the bodies had been dumped in the Tigris River, which runs by the palace compound. 
 
 The ISIS photographs appeared to have been taken at that location, the employee said. However, he said he had not spoken to any witnesses who claimed to have seen the executions or the victims’ bodies. 
 
 Ryan C. Crocker, a former ambassador to Iraq and a critic of America’s 2011 withdrawal from that nation after the two countries failed to sign a mutual security pact, said the atrocity claims, proven or not, made it more urgent than ever for Washington to become involved. 
 
 “What this administration has to do is get John Kerry on a plane right now, like we did when I was there, and sit down with Shia, Sunni and Kurdish leaders and help them get to a position of declared national unity. Iraqis have to stand together now,” Mr. Crocker said. Regarding the massacres, he said, “Whatever it is, however many people, it’s clearly an effort to ignite an Iraqi civil war.” 
 
 Political analysts here mostly agreed about the militants’ intent. “The problem now is that you are dealing with emotions and ISIS is trying to provoke the other side to take revenge,” said Ameer Jabbar al-Sa’aedi, a Baghdad-based analyst. “There are extremists among the Shia, too, and if they respond, they could begin killing and not exclude anyone. It would be just like what happened in 2006.” 
 
 Even though Ayatollah Sistani’s statement over the weekend was intended to call for restraint on the part of Shiites, it came after his call just a day before for every Iraqi to take up arms to support the government. 
 
 That appeal was expected to greatly accelerate the formation of volunteer groups to supplement Shiite militias — nominally to fight alongside the Iraqi Army. But during the worst of the sectarian bloodletting in Iraq, from 2005 through 2007, some such Shiite groups were deeply involved in violence that was killing as many as 1,000 civilians each week. 
 
 One militia leader, Abu Bakr al-Zubaidi, from a group called Asaib Al Haq, a hard-line offshoot of the Mahdi Army militia, said he was not surprised to hear of the executions. 
 
 “ISIS regards Shia as their eternal enemy, and they will kill whoever falls in their hands who is Shia, whether they are soldiers, grocers or even singers,” he said. “Our response to that is there will not be any living ISIS prisoner.” ||||| Earlier Monday, the United Nations said it had temporarily relocated 58 staff members from Baghdad to Amman, Jordan. Farhan Haq, a spokesman for Secretary General Ban Ki-moon, told reporters in New York that more United Nations staff members might be moved in coming days. 
 
 The new setbacks for the Iraqi government added urgency to demands from Iran and the United States — which have now both signaled a new willingness to cooperate on the crisis — that Mr. Maliki move quickly to reach out to Sunnis and Kurds and forge a united front against the Sunni extremists, who in the past week have brought much of the north and west of the country under their control. 
 
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 Mr. Maliki has publicly declared his confidence that the volunteers would help fill gaps in his beleaguered military, which has been decimated by desertions. Young Shiite men have enthusiastically signed up throughout Baghdad and southern Iraq, racing to the front lines with little training or preparation, since Iraq’s top Shiite cleric, Grand Ayatollah Ali al-Sistani, exhorted them on Friday to take up arms and defend the country. 
 
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 Yet the ambush, which occurred Sunday night near Samarra, about 70 miles north of Baghdad, raised questions about how effective such volunteers will be in fighting experienced insurgents. 
 
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 The volunteers had just left the northern town of Ishaqi and were heading south to reinforce Samarra, still held by the Iraqi Army but under pressure from Islamic State in Iraq and Syria, or ISIS, which has threatened to destroy its historic Shiite shrine. An attack on that shrine in 2006, during the height of the American-led invasion that toppled the Hussein regime, provoked bloody sectarian warfare nationwide. 
 
 Hidden in a small convoy of refrigerator trucks for the perilous journey through territory where ISIS is active, the volunteers were hit with a roadside bomb, said a Shiite militia leader, Abu Mujahid. At the same time, he said, “the militants came from nowhere and started shooting from everywhere and killed 28 volunteers.” 
 
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 At the morgue of the hospital in Samarra, an official said 29 dead were brought there, and that a further 190 volunteers were wounded in the attack. Mr. Mujahid put the wounded at 17. 
 
 Farther north, the fall of Tal Afar followed a two-day battle between the Iraqi military and the insurgents. The militants have now gained control of another city on the road to Syria through Nineveh Province, after the fall less than a week earlier of the province’s capital, Mosul, Iraq’s second-largest city, about 35 miles to the east of Tal Afar. 
 
 The Islamic State in Iraq and Syria militants claimed that along with taking Tal Afar, they had captured the commander of Iraqi Army forces in the city, Gen. Abu al-Waleed, and planned to execute him in a square in central Mosul. Residents said the militants used bullhorns to call people to the execution, but it never took place. General Waleed’s voice was later heard on Iraqi state television disputing the insurgents’ claims. “I am in good health and on the battlefield and will announce victory over ISIS in all of the territory of Tal Afar in the next few hours,” the channel quoted him as saying. 
 
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 Residents of Tal Afar, which has a population of 200,000, said most Shiite families had fled west, toward Sinjar, while Sunnis had gone east, toward Mosul. 
 
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 One of the first clashes also erupted on Monday between ISIS fighters and members of the Kurdish pesh merga militia, who have sought to avoid each other. A pesh merga convoy on the Kirkuk-Tikrit highway inadvertently strayed into a no man’s land and encountered an ISIS checkpoint, which fired at the convoy and wounded at least one Kurdish militia member. The convoy then turned around. 
 
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 In Geneva, the top human rights official of the United Nations added her voice to the growing alarm over summary executions carried out by Sunni militants in Iraq, asserting they had killed more than a dozen religious leaders in Mosul. 
 
 The official, Navi Pillay, the high commissioner for human rights, also said her own sources had corroborated ISIS claims that its fighters had massacred hundreds of Shiite soldiers in recent days. 
 
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 “This apparently systematic series of coldblooded executions, mostly conducted in various locations in the Tikrit area, almost certainly amounts to war crimes,” Ms. Pillay said in a statement. 
 
 In the capital, Brig. Gen. Saad Maan, the spokesman for the Baghdad Operation Command, held a news briefing to announce that the authorities had killed 56 insurgents in areas of western and southern Baghdad. He also denied reports by Al-Hadath Television, part of the Saudi-owned Arabiya television network, that the insurgents had made strikes near Baghdad International Airport. 
 
 “The airport is functional, and everything is normal,” General Maan said, adding that the authorities wanted Al-Hadath to be shut down because of its reports.
– As fighting rages today across Iraq, Washington is beginning to take action. About 50 to 100 Marines and Army personnel are now at the US embassy in Baghdad, and some embassy staff have been moved to other consular offices in Iraq and Jordan, CNN reports. Meanwhile, US Navy ships including the aircraft carrier USS George HW Bush have arrived in the Persian Gulf, NBC News reports. And the Wall Street Journal reports that the US is planning to begin direct talks with Iran this week about ways of curbing Sunni militants in Iraq. In other news: The militants who seized much of western and northern Iraq say they've recently executed 1,700 people, the New York Times reports. No official confirmation yet, but the Islamic State of Iraq and Syria posted gruesome images of massacre sites on Twitter. Most victims are reportedly Shiite Iraqi soldiers, but Sunnis affiliated with the government were among the dead. The Grand Ayatollah Ali al-Sistani revised the call to arms he issued Friday, apparently concerned about a possible wave of Sunni/Shiite reprisal killings. He urged Iraqis "to exert the highest level of self-restraint during this tumultuous period." Militants clashed with security forces near al-Khalis, northeast of Baghdad, and took over the town of Tal Afar, near the Syrian border. Sunni residents in Tal Afar say Shiite forces bombed their neighborhoods with mortar fire, Reuters reports. Two bomb attacks today killed up to 21 people in central Baghdad, one in a market full of volunteers assembled to join the fight against militants, the New York Times reports. See where ISIS militants came from, or how they became "insanely wealthy."