Syria conflict: US issues warning on chemicals plan
The US has warned that a Russian plan on Syrian chemical weapons must not be an excuse for "delays and avoidance".
US Secretary of State John Kerry said the plan must be "swift and verifiable" and warned its implementation would be "exceedingly difficult".
Syria earlier said it accepted the Russian plan to put the chemical weapons under international control.
The US, UK and France are to table a UN Security Council resolution but Russia has already indicated opposition.
The resolution will call on Syria to publicly declare that it has a chemical weapons programme, place it under international control and dismantle it.
UK Prime Minister David Cameron said the motion was designed to ensure that Russia's offer was "not a ruse".
"We need a proper timetable, process and consequences if it's not done," he said.
Mr Kerry said that if the UN were used as the vehicle for pursuing the Russian plan, it must not become a debating society.
But French Foreign Minister Laurent Fabius said he had spoken on Tuesday to Russian counterpart Sergei Lavrov, who told him that Moscow was not in favour of a binding resolution.
The motion would be tabled under Chapter 7 of the UN charter covering possible military and non-military action to restore peace.
The US alleges that Syrian government forces carried out a chemical weapons attack in Damascus on 21 August, killing 1,429 people.
The Syrian government blames the attack on rebels fighting to overthrow President Bashar al-Assad, in a conflict that the UN says has claimed some 100,000 lives.
Mr Kerry told a hearing of the House of Representatives Armed Services Committee the US was waiting for details of the Russian proposal, "but we're not waiting for long".
He said: "President Obama will take a hard look at it. But it has to be swift, it has to be real, it has to be verifiable.
"We have to show Syria, Russia and the world we are not going to fall for stalling tactics."
Mr Kerry urged Congress to stand by Mr Obama, saying the president was not asking for a declaration of war, simply for the power to show that the US "means what we say".
There have been few details so far of Russia's plan, but Mr Lavrov said earlier in Moscow that it was "preparing a concrete proposal which will be presented to all interested sides, including the US... a workable, specific, concrete plan".
Syrian Foreign Minister Walid Muallem, who is in Moscow, was quoted by Russian news agency Interfax as saying: "We held a very fruitful round of talks with [Mr Lavrov] yesterday and he proposed an initiative relating to chemical weapons. And in the evening, we agreed to the Russian initiative."
This would "remove the grounds for American aggression", he said.
Mr Muallem added: "We are convinced that the position of those striving for peace is much stronger than that of those trying to fuel war."
The US Senate had been expected to vote this week on a resolution authorising military force, but the Russian plan has led to a postponement.
Mr Kerry said that "nothing has changed with respect to our request for the Congress to take action" but that Mr Obama might want to discuss the timing of a vote with congressional leaders.
Mr Lavrov said the Russian initiative was "not a purely Russian initiative... it grew out of contacts we've had with the Americans".
Russian President Vladimir Putin and President Obama discussed the idea on the sidelines of a G20 summit last week, Mr Putin's spokesman said on Tuesday.
Mr Obama's prime-time television address to the nation is still scheduled to go ahead on Tuesday evening, and the White House said he still planned to use it to argue that Congress should authorise the use of force if required.
Republican Senator John McCain, who has been an advocate of military action, said on Tuesday that a bipartisan group of senators was now working on a new resolution that would set Syria a specific period of time to turn over its chemical weapons.
Senator McCain told CBS he was "extremely sceptical" about the Russian proposal but that "to not pursue this option would be a mistake".
Opinion polls suggest that a majority of voters are opposed to Mr Obama's calls for intervention in Syria.
According to a survey by the Associated Press news agency, 61% of Americans want Congress to vote against authorisation for military strikes.
Watch President Obama's address to the nation live on the BBC News website at 21:00 EDT on Tuesday (01:00 GMT/02:00 BST Wednesday).