A Russian proposal for Syria to hand over its chemical weapons supply should be taken seriously, the prime minister said today.
David Cameron said the UK would table a resolution to the UN security council alongside France and the US, in order to "test out" Russia's proposal.
"It is an interesting proposal and if it is a serious one then it is one that we should take very seriously because it could achieve a major goal we have to get rid of chemical weapons," he told MPs during a two-hour grilling before the Commons' liaison committee.
"We have to bear in mind that Syria has the biggest supply of chemical weapons anywhere in the world."
Cameron said the allies needed to be careful that the proposal was not a "ruse" by the Russians.
"We must be sceptical, we must be careful and enter this with a hard head because we do not want this to be a delaying tactic, some ruse just to buy time for a regime that must act on chemical weapons," he added, insisting: "We should not forget that a war crime has been committed."
Earlier, US president Barack Obama described the proposal as a "potential breakthrough" and said he would be willing to put his military plans on hold if the Syrian regime complied.
The security council resolution is expected to include a timetable and a "threshold" for action by Syrian president Bashar al-Assad.
Shadow foreign secretary Douglas Alexander said: “While this offer deserves a cautious welcome, the international community must work to establish whether this latest proposal is a serious initiative.
“Primary responsibility now lies with Assad who must take clear and verifiable steps to show that he is serious about handing over chemical weapons.”