Chemical weapons experts say they have gathered "valuable" evidence on a suspected chemical weapons attack near Damascus, despite coming under sniper fire yesterday.
The UN inspection team's lead vehicle was "deliberately shot at multiple times" as they left a government checkpoint in the Syrian capital.
None of the UN inspectors, who were dressed in body armour, was injured in the attack, which came after two mortar bombs landed close to their hotel. The vehicle's tyres and front window were damaged.
After the shooting, the UN inspectors were able to change vehicles and go ahead with meeting victims of the alleged chemical attack, taking samples for testing.
UN Secretary General Ban Ki-Moon did not apportion blame but did make a "strong complaint" to Syria.
The team will continue their work today.
Reuters carried this video of the UN inspection team speaking to survivors:
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".
But US Secretary Of State John Kerry said chemical weapons had been used and evidence had been destroyed.
White House spokesman Jay Carney added that there was "very little doubt" in the Obama administration's mind that the Syrian government was responsible for using chemical weapons.
The Syrian opposition claims up to 1,300 people were killed, while Doctors Without Borders said 355 people died in hospital from "neurotoxic" symptoms.
Mr Ban 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."
The international community continues to consider its response to the crisis.
British Prime Minister David Cameron will chair of a meeting of the UK's National Security Committee on Wednesday after discussing the crisis with Russian President Vladamir Putin by telephone.
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.
"Syria will never become a Western ‘puppet’ state" - Assad
"Failure awaits the United States as in all previous wars it has unleashed," the Syrian president said in an interview with Russian newspaper Izvestia.
Bashar al Assad spoke to reporters from Russia's Izvestia newspaper
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."
Mr Assad received backing from two of his main allies, with Russia's Foreign Minister Sergei Lavrov warning that the use of force without a UN mandate would violate international law.
Meanwhile, Iran's Supreme Leader Ayatollah Ali Khamenei blamed countries outside the Middle East for the turmoil and said states in the region backing the Syrian opposition would be damaged by the conflict.
"The main reason behind the status quo in the region is interference from outside the region," the state news agency Fars quoted Khamenei as saying in a meeting with Oman's Sultan Qaboos.
