Russia says it will push Syria to place its chemical weapons under international control.

The surprise announcement by Russian Foreign Minister Sergey Lavrov came a few hours after US Secretary of State John Kerry said that Syrian president Bashar Assad could resolve the crisis by surrendering control of "every single bit" of his arsenal to the international community by the end of the week.

Mr Kerry added that he thought Assad "isn't about to do it," but Mr Lavrov, who just ended a round of talks in Moscow with his Syrian counterpart Walid al-Moallem, said that Moscow would try to convince the Syrians.

"If the establishment of international control over chemical weapons in that country would allow avoiding strikes, we will immediately start working with Damascus," Mr Lavrov said.

"We are calling on the Syrian leadership to not only agree on placing chemical weapons storage sites under international control, but also on its subsequent destruction and fully joining the treaty on prohibition of chemical weapons," he said.

Syria welcomed the move by Russia but did not offer a time frame or any other specifics.

A statement by Mr al-Moallem appeared to mark the first official acknowledgement by Damascus that it possesses chemical weapons and reflected what appeared to be an attempt to avoid a US military attack.

"Syria welcomes the Russian proposal out of concern for the lives of the Syrian people, the security of our country and because it believes in the wisdom of the Russian leadership that seeks to avert American aggression against our people," Mr al-Moallem said.

But it remained to be seen whether the statement represented a genuine goodwill gesture by Syria or simply an attempt to buy time. Mr Lavrov said that he has already handed over the proposal to Mr al-Moallem and expects a "quick, and, hopefully, positive answer."

US officials said they will take a "hard look" at the proposal but it would be considered with "serious scepticism" because it might be a stalling tactic.