A UN security resolution is to be tabled on Tuesday night by Britain, France and the US to test whether Russian support for a proposal to force Syria to make public its chemical weapons programme is serious or a "ruse", David Cameron has said.
The British prime minister, who spoke to Barack Obama on Tuesday afternoon after Russia said Syria should place its chemical weapons under international control, said the three allies would use the UN to see whether Moscow was embarking on a delaying tactic.
Cameron confirmed to MPs that Britain, France and the US would be tabling a UN security council resolution on Tuesday night a day after the Russian foreign minister, Sergei Lavrov, said Moscow was examining proposals with Damascus to hand over its weapons to international control. Lavrov made his comments after John Kerry, the US secretary of state, said the Assad regime could avoid military strikes if it handed over its chemical weapons in a week.
Lavrov said Moscow and Damascus were working on a plan in consultation with the UN secretary general, Ban Ki-moon, and the Organisation for the Prohibition of Chemical Weapons (OPCW).
Ban said he would urge the security council to demand the immediate transfer of Syria's chemical weapons to internationally controlled sites inside the country where they could be destroyed.
Syrian state television quoted the Syrian prime minister, Wael al-Halki, as saying President Bashar al-Assad's government backed the initiative, confirming what his foreign minister had earlier told the speaker of the Russian parliament.
"We held a very fruitful round of talks with foreign minister Sergei Lavrov yesterday, and he proposed an initiative relating to chemical weapons. And in the evening we agreed to the Russian initiative," the Syrian foreign minister, Walid al-Moualem, told the Interfax news agency. He added Syria had agreed because this would "remove grounds for American aggression".
Cameron said a timetable would have to be agreed for the removal and destruction of the weapons. "The Russian response to what Secretary of State Kerry said yesterday was interesting. Let's test it out. If we can achieve the removal and the destruction of the biggest chemical weapons arsenal in the world that would be a significant step forward," Cameron said.
"It is definitely worth exploring. But we must be sceptical, we must be careful, we must enter this with a very hard head and some pretty cool calculations. We do not want this to be some delaying tactic, some ruse to buy time for a regime that must act on chemical weapons."
The prime minister said he had spoken to Obama briefly at the G20 in Saint Petersburg last week about plans for the removal and destruction of chemical weapons. This suggested that Kerry's remarks may not have been off the cuff.
But he said of the Russian proposal: "What is important is to make sure this isn't some delaying tactic, that this isn't some ruse. If it this is a serious proposal then we should act accordingly. I think a UNSCR [security council resolution] is a good idea. In that resolution it is quite important that we have some clarity about thresholds. We know there is a proper timetable for doing this. We need to know there would be a proper process for doing it and, crucially, there would have to be consequences if it wasn't done.
"Of course we should be sceptical, of course we should not forget a war crime has been committed. But this could be a major step forward, but we need to test it out properly."
Earlier the French foreign minister, Laurent Fabius, said France had reacted with "interest but also with caution" to the Russian proposal that Syria place its weapons under international control.
Paris, still wary of falling into a trap or "diversionary" tactic, had therefore decided to push immediately for a UN resolution under chapter 7 of the UN charter, which would make "concrete" the notion of the Syrian regime opening up its chemical weapons arsenal for inspection and dismantlement, Fabius said.
Keen to regain the initiative on the Syria weapons issue after Moscow's proposal, France stipulated the five conditions of the resolution that would be put to the 15-nation UN body. Fabius said the resolution would condemn the "chemical massacre" committed on 21 August "by the Syrian regime".
It would demand that the Syrian regime "shed all light" on its chemical weapons programme without delay, placing it under international control and dismantling it. Syria must put in place a complete procedure to allow full inspections of chemical weapons and must become party to the chemical weapons convention. There would be extremely serious consequences if these obligations were violated.
Finally, "the authors" of the 21 August chemical attacks must face legal sanctions via the international criminal court (ICC).
It was not clear whether Russia would go along with a chapter 7 resolution, as it would open the door to punitive measures possibly including force. Furthermore, Russia and China have continually resisted the Syrian conflict being referred to the ICC for investigations of war crimes.
Asked if the UN initiative meant the option of military force was officially off the agenda, Fabius said Paris would explore the possibility of full Syrian chemical weapons control in good faith but with caution, and "all options are still on the table".
He said: "The Syrian people have suffered too much" and France was seeking a "firm, precise and verifiable" response to the chemical weapons use.
"From the start, France's aim has been to limit the chemical weapons threat and protect the Syrian people," he said.