Media playback is unsupported on your device Media caption The BBC's Yolande Knell: "The UN has always said the safety of its team is paramount" 
 
 Unidentified snipers have opened fire on a convoy of UN experts investigating suspected chemical weapons attacks in Syria's capital, the UN has said. 
 
 One car was shot at "multiple times", forcing the convoy to turn back. 
 
 Syrian state media blamed opposition "terrorists" for the attack, though the claim could not be verified. 
 
 The UN team later resumed its mission, entering the western district of Muadhamiya to gather evidence, before returning to central Damascus. 
 
 Hundreds died in alleged attacks on Wednesday in five districts near Damascus. 
 
 The US said there was little doubt that Syrian forces used chemical weapons in the attacks, which reportedly killed more than 300 people in rebel-held areas. 
 
 Syrian President Bashar al-Assad dismissed the accusation as "an insult to common sense" and warned the US against military intervention. 
 
 "If someone is dreaming of making Syria a puppet of the West, then this will not happen," he told the Russian newspaper Izvestiya. 
 
 'Intimidation' 
 
 The 20-member UN inspection team has been in Syria since 18 August to look into three earlier suspected chemical attacks. They were given permission on Sunday to examine the Damascus locations. 
 
 Image caption The UN inspectors have been talking to doctors in Muadhamiya 
 
 The experts intend to take soil, blood, urine and tissue samples for laboratory testing but they are unlikely to apportion blame for any of the attacks. 
 
 Video footage posted online appears to show UN inspectors in Muadhamiya taking samples and talking to residents. 
 
 They went to a Red Crescent centre and spoke to doctors, opposition activists said. 
 
 On the video, which the BBC has not been able to fully authenticate, one resident is heard telling an inspector of heavy raids on the district, with "over 600 canister strikes...12 tanks, 100 soldiers". 
 
 Shortly after setting out from their hotel in Damascus, the inspectors' cars came under fire "multiple times by unidentified snipers", according to a statement from the UN. 
 
 Analysis Whitehall officials say no firm decision is likely to be taken on how Britain will respond to last week's alleged chemical attack in Syria until at least Wednesday. That is when UK PM David Cameron will be chairing a session of the National Security Council, attended by military and intelligence chiefs and senior ministers. It follows intense consultations between London and Washington with Downing Street keen to stress the two countries are acting in concert. Any military response, if it is decided on, is most likely to be confined to a one-off or limited guided missile strikes on selected Syrian military targets using Tomahawk cruise missiles fired from US Navy warships stationed hundreds of miles away in the eastern Mediterranean. US vessels there are reported to have around 400 such missiles onboard, while a Royal Navy submarine in the region can also carry cruise missiles. But Russia, Syria and Iran have all issued strong warnings against any western military action. 
 
 The team returned safely back to the government checkpoint before setting out again. 
 
 The convoy was "deliberately targeted" and it seemed someone was trying to intimidate the team, the UN Secretary General's spokesman, Farhan Haq, told the BBC. 
 
 The inspectors have now returned to their hotel and are expected to resume their work on Tuesday. 
 
 Military action 
 
 A year ago, US President Barack Obama said the use of chemical weapons by the Syrian government would be "a red line" that could trigger US military action. 
 
 Washington has recently bolstered its naval presence in the eastern Mediterranean, and military leaders from the US, UK and their allies are meeting in Jordan. 
 
 But the UN Security Council remains divided, with China and Russia appearing unlikely to drop their objection to stricter sanctions on Mr Assad's government. 
 
 Chinese Foreign Minister Wang Yi said on Monday that diplomats should be cautious in dealing with the chemical weapons issue, and Moscow warned Western nations not to prejudge the outcome of the inspections. 
 
 Western politicians have begun to suggest taking action outside of the UN system. 
 
 UK Foreign Secretary William Hague told the BBC that action could be taken without UN approval if there was "great humanitarian need" in Syria. 
 
 His French counterpart Laurent Fabius suggested the UN Security Council could be bypassed "in certain circumstances". 
 
 Media playback is unsupported on your device Media caption William Hague: UN Security Council has not shouldered its responsibilities 
 
 But in his latest comments on the crisis, Russian Foreign Minister Sergei Lavrov said any intervention in Syria without a UN mandate would be a "grave violation of international law". 
 
 The West, he told a news conference in Moscow, had not been able to come up with any proof of chemical weapons use while "saying at the same time that the red line has been crossed and there can be no delay". 
 
 'Neurotoxic symptoms' 
 
 Western officials were unimpressed with Syria's decision to allow in the UN experts. 
 
 Mr Hague said evidence could have been tampered with, degraded or destroyed in the five days since the attack. 
 
 A senior White House official, quoted by AP news agency, dismissed the visit as "too late to be credible". 
 
 Medecins Sans Frontieres (MSF) said on Saturday that three hospitals it supports in the Damascus area had treated about 3,600 patients with "neurotoxic symptoms" on Wednesday morning, of whom 355 had died. 
 
 While MSF said it could not "scientifically confirm" the use of chemical weapons, staff at the hospitals described a large number of patients arriving in the space of less than three hours with symptoms including convulsions, pinpoint pupils and breathing problems. 
 
 Syria's security forces are widely believed to possess large undeclared stockpiles of mustard gas and sarin nerve agent. 
 
 It is one of seven countries that have not joined the 1997 convention banning chemical weapons. ||||| WASHINGTON/BEIRUT The United States put Syrian President Bashar al-Assad on notice on Monday that it believes he was responsible for using chemical weapons against civilians last week in what Secretary of State John Kerry called a "moral obscenity." 
 
 "President (Barack) Obama believes there must be accountability for those who would use the world's most heinous weapons against the world's most vulnerable people," Kerry said in the most forceful U.S. reaction yet to the August 21 attack. 
 
 Speaking after U.N. chemical weapons experts came under sniper fire on their way to investigate the scene of the attack, White House spokesman Jay Carney said the use of chemical weapons was undeniable and "there is very little doubt in our mind that the Syrian regime is culpable." 
 
 Kerry said Obama was consulting with allies before he decides on how to respond. 
 
 "What we saw in Syria last week should shock the conscience of the world," Kerry told reporters. 
 
 "The indiscriminate slaughter of civilians, the killing of women and children and innocent bystanders by chemical weapons is a moral obscenity. By any standard, it is inexcusable. And despite the excuses and equivocations that some have manufactured, it is undeniable." 
 
 Military chiefs from the United States and its European and Middle Eastern allies met in Jordan for what could be a council of war, should they decide to punish Assad, who has denied using chemical weapons and blamed rebels for staging such attacks. 
 
 Many hundreds of people died in Damascus suburbs in what appears to have been the worst chemical weapons attack since Iraqi leader Saddam Hussein fatally gassed thousands of Kurds in 1988. 
 
 U.N. investigators crossed the front line from the center of the capital, which remains under Assad's control, to inspect the Mouadamiya suburb, one of at least four neighborhoods hit by the poison gas before dawn last Wednesday. 
 
 The United Nations said one vehicle in its convoy was crippled by gunshots fired by "unidentified snipers." The team continued on after turning back for a replacement car. 
 
 Syrian state television blamed rebel "terrorists" for the shooting. The opposition blamed pro-Assad militiamen. 
 
 "I am with the team now," a doctor who uses the name Abu Karam told Reuters by telephone from Mouadamiya. "We are in the Rawda mosque and they are meeting with the wounded. Our medics and the inspectors are talking to the patients and taking samples from the victims now." 
 
 Wassim al-Ahmad, an opposition activist, said members of the Free Syrian Army umbrella rebel organization and the opposition's Mouadamiya Local Council were accompanying the inspectors on their tour of the suburb. 
 
 "The inspectors are now examining victims being treated at a makeshift hospital in Mouadamiya and are taking blood samples from them," Ahmad said. 
 
 INTERVIEWING SURVIVORS 
 
 Video filmed at the site showed inspectors in black and blue body armor and blue U.N. helmets walking through a street as curious onlookers came up to watch. 
 
 They shook hands with men who appeared to be rebels wearing camouflage vests, and were accompanied by doctors and residents. The group descended into the basement of a building where they were told injured survivors were being treated to protect them from more shelling. Another video showed an inspector interviewing a patient and taking notes. 
 
 Activists say at least 80 people were killed in Mouadamiya when the district was hit with poison gas. Hundreds of people also were killed in three other rebel-held districts - Irbin, Ain Tarma and Jobar. 
 
 An opposition activist said a large crowd of people gathered to air their grievances to the U.N. inspectors, who planned to take samples from corpses. 
 
 The inspectors later returned to their hotel and, within an hour, residents reported the shelling of Mouadamiya had resumed. 
 
 The decision to proceed with the mission despite coming under attack thwarted an apparent attempt to halt the inspectors' work before it began. 
 
 "The first vehicle of the Chemical Weapons Investigation Team was deliberately shot at multiple times by unidentified snipers in the buffer zone area," the United Nations said in a statement. "It has to be stressed again that all sides need to extend their cooperation so that the team can safely carry out their important work." 
 
 The inspectors had been stuck in a downtown hotel since the attack, waiting five days for government permission to visit the scene a few miles away. They had arrived three days before the incident, with a mandate to investigate earlier reports of more limited chemical weapons use. 
 
 ASSAD TOO LATE 
 
 Kerry said Assad's decision to finally allow access was too late to be credible. "That is not the behavior of a government that has nothing to hide," Kerry said, adding that Assad's forces had also destroyed evidence by shelling the area. 
 
 "Our sense of basic humanity is offended not only by this cowardly crime, but also by the cynical attempt to cover it up," Kerry said. 
 
 He said the U.N. inspectors could at most confirm that chemical weapons were used, not who used them, but that it was Assad's government that has such weapons and the means of delivering them. He said Washington had additional information on the attack that it would make known soon. 
 
 Washington and its allies say they worry that the time that has elapsed, and continuous shelling by Assad's forces of the affected areas, could make it impossible for the inspectors to collect evidence. The United Nations said Secretary-General Ban Ki-moon was confident the team could get the data it needs. 
 
 Speculation has been mounting that Western countries will order some kind of military response to an incident that took place a year after Obama declared the use of chemical weapons a "red line" that would require strong action. 
 
 With his international credibility seen increasingly on the line, Obama could opt for limited measures such as cruise missile strikes to punish Assad and seek to deter further chemical attacks, without dragging Washington deeper into the war. The United States has started a naval buildup in the region to be ready for Obama's decision. 
 
 In neighboring Israel, citizens have been queuing up for gas masks in case Assad responds to a Western attack by firing on Israel, as Iraq's Saddam did in 1991. 
 
 PHONE CONSULTATIONS 
 
 With tensions rising over Syria, British Prime Minister David Cameron cut short a holiday to lead a top-level security meeting. Obama, Cameron and French President Francois Hollande all spoke to each other and other allies in the past few days in a flurry of phone calls. Cameron also called Russian President Vladimir Putin on Monday. 
 
 Several NATO countries have issued statements pledging a response, although none has been specific about what is planned. 
 
 Top military officers of the United States, Britain, France, other NATO allies and the main anti-Assad countries in the region, including Saudi Arabia and Turkey, met in Jordan on Monday to discuss Syria, diplomats there said. 
 
 The conference was planned but took on new significance because of the latest events, the diplomats said. 
 
 The chairman of the U.S. Joint Chiefs of Staff, Martin Dempsey, a co-host of the meeting with his Jordanian counterpart, has been one of the voices in Washington urging caution and emphasizing the costs of a full-scale military intervention in a war in the heart of the Middle East. 
 
 Obama, who withdrew U.S. troops from Iraq and is winding down the conflict in Afghanistan, is reluctant to involve the United States in another war. A Reuters/Ipsos poll published on Saturday showed about 60 percent of Americans opposed U.S. military intervention, while only 9 percent thought Obama should act. 
 
 ASSAD DEFIANT 
 
 Assad denies the accusations that his forces used chemical weapons and said the United States would be defeated if it intervened in his country. 
 
 "Would any state use chemicals or any other weapons of mass destruction in a place where its own forces are concentrated? That would go against elementary logic," he told the Russian newspaper Izvestia. "Failure awaits the United States as in all previous wars it has unleashed, starting with Vietnam and up to the present day." 
 
 Russia, Assad's main arms supplier and diplomatic defender in the U.N. Security Council, says rebels may have been behind the chemical attack. Foreign Minister Sergei Lavrov said any intervention in Syria without a Security Council resolution would be a grave violation of international law. 
 
 French Foreign Minister Laurent Fabius noted that Russia and China would probably veto a U.N. Security Council vote to allow strikes against Syria. But British Foreign Secretary William Hague said it would still be possible to respond to a chemical weapons attack without the Security Council's permission. 
 
 There are precedents. In 1999 NATO attacked Serbia, a Russian ally, without a Security Council resolution, arguing that action was needed to protect civilians in Kosovo. 
 
 Turkey, a NATO ally and major backer of Syria's opposition, said it would join any international coalition even if a decision for action could not be reached at the United Nations. 
 
 (Additional reporting by Mariam Karouny in Beirut, Khaled Yacoub Oweis in Amman, John Irish in Paris, Katya Golubkova in Moscow, Steve Holland and Paul Eckert in Washington.; Writing by Matt Spetalnick and Claudia Parsons; Editing by Bill Trott and Christopher Wilson) ||||| Image caption The convoy carrying UN chemical weapons inspectors to the sites was targeted by snipers 
 
 Diplomatic pressure on Syria has failed and the UK is considering its response to a suspected chemical attack, Foreign Secretary William Hague says. 
 
 He told the BBC it would be possible for the UK and its allies to respond without the UN's unanimous backing. 
 
 In Syria, UN inspectors visited the site of the suspected attack after their convoy was shot at by snipers. 
 
 The PM is cutting his holiday short and is expected to hold a National Security Council meeting on Wednesday. 
 
 Deputy Prime Minister Nick Clegg has also cancelled a visit to Afghanistan to meet British troops. 
 
 Downing Street said a decision on whether to recall Parliament would be made on Tuesday. 
 
 The suspected chemical attack took place on Wednesday near the Syrian capital Damascus, and reportedly killed more than 300 people. 
 
 Weapons inspectors carried out tests at the scene on Monday after unidentified snipers shot at one of their vehicles, a UN spokesman said. 
 
 Media playback is unsupported on your device Media caption William Hague: UN Security Council has not shouldered its responsibilities 
 
 Mr Hague told BBC Radio 4's Today programme while he could not go into options or a timetable for action, he was not "going to rule anything in or out". 
 
 "We, the United States, many other countries including France, are clear that we can't allow the idea in the 21st century that chemical weapons can be used with impunity," he said. 
 
 A Downing Street spokesman said Prime Minister David Cameron had called Russia's President Vladimir Putin on Monday afternoon to discuss Syria and that they had reiterated the position that the use of chemical weapons should merit a "serious response" from the international community. 
 
 But while Mr Cameron "made clear there was little doubt" the attack was carried out by the Syrian regime, Mr Putin "said they did not have evidence of whether a chemical weapons attack had taken place or who was responsible," the spokesman said. 
 
 MPs are due to return to the Commons on 2 September but there have been demands for Parliament to be recalled. 
 
 Analysis Whitehall officials say no firm decision is likely to be taken on how Britain will respond to last week's alleged chemical attack in Syria until at least Wednesday. That is when David Cameron will be chairing a session of the National Security Council, attended by military and intelligence chiefs and senior ministers. It follows intense consultations between London and Washington with Downing Street keen to stress the two countries are acting in concert. Any military response, if it's decided on, is most likely to be confined to a one-off or limited guided missile strikes on selected Syrian military targets using Tomahawk cruise missiles fired from US Navy warships stationed hundreds of miles away in the eastern Mediterranean. US vessels there are reported to have about 400 such missiles onboard, while a Royal Navy submarine in the region can also carry cruise missiles. But Russia, Syria and Iran have all issued strong warnings against any western military action. 
 
 Labour's shadow foreign secretary Douglas Alexander said he would "expect the prime minister to make his case to Parliament" before a decision was made about UK involvement. 
 
 The prime minister also had phone calls with other leaders, including US President Barack Obama, this weekend, where they agreed on the need to take "strong action". 
 
 He will return several days early from his holiday in Cornwall with his family so he can chair Wednesday's high-level security briefing of senior ministers and defence and intelligence chiefs. 
 
 It is understood the most likely military response would be a one-off or limited guided missile strikes on Syrian military targets fired from US Navy warships, says BBC security correspondent Frank Gardner. 
 
 Prof Michael Clarke, of the Royal United Services Institute, said: "Military advice to politicians in the US and the UK is 'don't think you can dabble in this - you have to go in with both feet'". 
 
 He told the BBC's PM programme limited air strikes might inconvenience the regime but were no guarantee you could stop it. 
 
 Other options - such as a no-fly zone or a safe haven - would have to be led by the US, and at the moment most of the "sabre-rattling" was coming from France and the UK - not the US, he added. 
 
 Whitehall officials have told the BBC the next key decisions would probably be taken at Wednesday's National Security Council meeting. 
 
 'Humanitarian need' 
 
 Mr Hague said diplomatic methods to resolve the civil war in Syria had "failed so far". 
 
 Media playback is unsupported on your device Media caption Russian Foreign Minister Sergei Lavrov: "They [the West] have not been able to come up with any proof but are saying at the same time that the red line has been crossed" 
 
 He said the UN Security Council, split over Syria, had not "shouldered its responsibilities". 
 
 The council is made up of 15 members including permanent members China, Russia, France, the US and the UK which have the power to veto any resolution. 
 
 But any action could be taken "without complete unity on the UN Security Council", he said. 
 
 He said a response could be "based on great humanitarian need and distress" and "in accordance with international law". 
 
 The foreign secretary said the suspected chemical attack was carried out by Syrian President Bashar al-Assad's regime but it blames rebel forces saying footage of the attack was "fabricated".
– Syria may have given UN inspectors the OK to access the site of last week's alleged chemical weapons attack, but inspections are not off to a great start. A UN rep confirms that one of the team's vehicles was "deliberately shot at multiple times" by unidentified snipers in Damascus; all are safe. The shooting reportedly occurred in the buffer zone between rebel- and government-controlled territory, and the team will head back to the area once it replaces its vehicle, reports the AP. The Syrian government, for its part, has already blamed "terrorists," reports CNN. More: Once they finally reach the site of last week's alleged attack, UN inspectors will spend two days taking soil, blood, urine, and tissue samples, reports the BBC. But Reuters reports that the US and its allies aren't expecting much: They believe the regime's offer to allow inspectors to the site came too late and any remaining evidence has probably been destroyed by heavy shelling. To wit, a senior White House official dismissed the visit as "too late to be credible." Assad, meanwhile, says that any American attempt at military intervention will be doomed to fail. "Failure awaits the United States as in all previous wars it has unleashed, starting with Vietnam and up to the present day," he said in an interview with a Russian newspaper. UN chief Ban Ki-moon warns that "every hour counts" in determining the facts of what was a "major and terrible incident," reports the Guardian. "We cannot allow impunity in what appears to be a grave crime against humanity," he said. But the UN Security Council, which is split on the issue, has already failed to shoulder its responsibilities and the UK and its allies may have to take action without its approval, Britain's foreign minister says. "Is it possible to respond to chemical weapons without complete unity on the UN Security Council?" William Hague tells the BBC. "I would argue yes it is, otherwise it might be impossible to respond to such outrages."