By William James and Andrew Osborn
LONDON, Sept 10 (Reuters) - Britain, France and the United States will try to win support for a tough resolution on Syrian chemical weapons in the United Nations Security Council later on Tuesday, said British Prime Minister David Cameron.
Cameron had earlier said that the three countries would formally submit such a resolution later on Tuesday, but a British government source familiar with the matter told Reuters it would take a little longer before that could happen.
Detailed discussions about a draft resolution among the U.N. Security Council's five permanent members could go on for the next 24 hours, the source said, and only then could a resolution be formally submitted.
"The prize is potentially ridding the world of the single largest stock of chemical weapons," the source said, saying Britain and others had a duty to try to achieve that despite being sceptical about Syrian promises.
Syria on Tuesday accepted a Russian proposal to surrender its chemical weapons in order to win a possible reprieve from punitive U.S. military strikes which U.S. President Barack Obama has floated as a way of preventing a repeat of a suspected chemical attack on Aug. 21.
Cameron, who said he had spoken to Obama about the issue earlier on Tuesday, told lawmakers: "If this is a serious proposal then we should act accordingly and I think a U.N. Security Council resolution is a good idea."
"In that resolution I think it's quite important that we have some clarity about thresholds. We need to know that there's a proper timetable for doing this, we need to know there'd be a proper process for doing it, and crucially there'd have to be consequences if it wasn't done."
Cameron said the world needed to test how genuine the Russian proposal to place Syria's chemical weapons under international control was, saying it was important to make sure the idea wasn't "some delaying tactic, some ruse".
British Foreign Secretary William Hague said separately that time was short to try to ensure that the Syrian offer to surrender its chemical arms was credible, noting that President Bashar al-Assad's government had "consistently failed to match promises with action".