Weapons inspectors investigating an alleged chemical attack in Damascus have been shot at by snipers, a spokesman for the UN has said.
The team's lead vehicle was "deliberately shot at multiple times" as they left a government checkpoint during a visit to part of the city where hundreds of people were allegedly killed, Martin Nesirky told Sky News.
None of the inspectors, who were dressed in body armour, are believed to have been injured in the attack, which came after two mortar bombs landed close to their hotel.
"The inspectors are determined to carry out the mission they are mandated to carry out," Mr Nesirky said.
"But it's obvious that all sides need to extend their co-operation so they can conduct this work safely."
Mr Nesirky said it was not clear who was responsible for the sniper attack, although Bashar al Assad's regime blamed the bombings on rebel fighters.
After the shooting, the UN inspectors were able to change vehicles and are now meeting victims of the alleged chemical attack.
The Assad regime said the inspections in Zamalka and Ein Tarma districts will prove allegations that chemical weapons were used against civilians, including children, were "lies".
The opposition claimed 1,300 people were killed, while Doctors Without Borders said 355 people died in hospital from "neurotoxic" symptoms.
UN Secretary-General Ban Ki-Moon said the people of Syria deserved to know the truth, adding: "We cannot allow impunity in what appears to be a grave crime against humanity."
However, defence expert Chris Bellamy told Sky News that while the UN inspection may reveal whether chemical weapons were used, it may not identify who they were used by.
"If that's the case, we would need another investigation to identify who fired the shells," he said.
The international community continues to consider its response to the crisis, with the Foreign Secretary warning military action may be the only remaining option.
William Hague said Britain and other countries could respond to the alleged attack without the unanimous backing of the UN, telling the BBC: "Otherwise it might be impossible to respond to such outrages, such crimes."
His comments came as David Cameron announced he was cutting short his holiday to chair a meeting of the UK's National Security Committee.
Shadow foreign secretary Douglas Alexander urged the Prime Minister to recall Parliament to "make his case in advance of a decision being made".
A Downing Street spokesman insisted no decisions had been taken on military action and said there was no clear timetable.
Meanwhile, French politicians are preparing to meet "in the coming days" to decide whether to respond with force, according to the country's foreign minister Laurent Fabius.
There is mounting speculation that France, together with Britain and the US, could back limited airstrikes to demonstrate that deployment of chemical weapons will not be tolerated.
However, Mr Assad said military intervention by the US would fail.
"Failure awaits the United States as in all previous wars it has unleashed," the Syrian president said in an interview with Russian newspaper Izvestia.
Describing the chemical weapons accusations as "nonsense", Mr Assad added: "Would any state use chemical or any other weapons of mass destruction in a place where its own forces are concentrated? That would go against elementary logic.
"Accusations of this kind are entirely political and the reason for them is the government forces' series of victories over the terrorists."http://news.sky.com/story/1133285/syria-un-inspectors-shot-at-by-snipers