A US-Russian plan to eliminate Syria's chemical weapons gained China's support Sunday, easing its route towards the UN Security Council and hiking pressure on Damascus to act within days.
President Barack Obama warned the United States, which has threatened to launch military strikes against Syria in response to chemical attacks that killed hundreds last month, "remains prepared to act".
The ambitious plan to dismantle and destroy Syria's chemical arms by mid-2014 was thrashed out during three days of talks in Geneva between US Secretary of State John Kerry and his Russian counterpart Sergei Lavrov.
It gives Syrian President Bashar al-Assad a week to hand over details of his regime's stockpile of the internationally banned arms in order to avert unspecified sanctions and the threat of US-led military strikes.
China, a veto-wielding permanent member of the Security Council, welcomed the agreement.
"The Chinese side welcomes the general agreement between the US and Russia. This agreement will enable tensions in Syria to be eased," Foreign Minister Wang Yi said at a meeting with his visiting French counterpart Laurent Fabius.
But the deal has already been rejected by rebel forces who warned it would not halt the Syria conflict that has killed more than 110,000 people and displaced millions in two and a half years.
"We cannot accept any part of this initiative," said Free Syrian Army chief General Selim Idriss.
"Are we Syrians supposed to wait until mid-2014, to continue being killed every day and to accept (the deal) just because the chemical arms will be destroyed in 2014?"
Kicking off a flurry of diplomatic activity, Kerry flies to Israel on Sunday to brief Prime Minister Benjamin Netanyahu about the deal and discuss the Middle East peace process.
He will travel to Paris for a Monday meeting with Fabius and British Foreign Secretary William Hague, as well as the Saudi Foreign Minister Saud al-Faisal.
Announcing the deal on Saturday, Kerry said Assad's regime must provide "immediate and unfettered" access to inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW).
"The inspectors must be on the ground no later than November... and the goal is to establish the removal by halfway through next year," said Kerry, flanked by Lavrov at a Geneva news conference.
Obama said the pressure was now on Assad to deliver, but influential Senators John McCain and Lindsey Graham said the agreement was a debacle.
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The two Republican lawmakers voiced fear Washington's friends and foes alike would view the agreement as an "act of provocative weakness on America's part".
Kerry said the agreed steps would be encapsulated in a Security Council resolution drawn up under Chapter Seven of the UN charter, which provides for enforcement through sanctions, including the possible use of military force.
But with Russia strongly opposed to the use of military threats against its long-term ally Syria and also wielding a veto on the Council, Kerry acknowledged it was "impossible to have a pre-agreement" on what would happen in the event of non-compliance.
Lavrov hailed the accord as an "excellent" agreement "whose significance is hard to overestimate."
The Russian foreign minister will hold talks on Tuesday with his French counterpart amid an intense few days of negotiations between the five permanent members of the Security Council.
Both China and Russia have consistently blocked resolutions at the UN to sanction the Syrian regime.
France has been one of Washington's closest allies in urging military action in response to an August 21 chemical attack on the outskirts of Damascus blamed by Washington and others on Syria's government.
The British parliament has voted against participating in any military action against Assad.
Fighting on the ground in Syria has continued unabated, with rebel and regime forces engaged in a fierce battle for control of the historic Christian town of Maalula, near Damascus.
Kerry said the Syrian war could only be ended through negotiations, and promised to meet with Lavrov again soon to try to breathe life into planned peace talks between the regime and the opposition.
Washington and Moscow hope to secure a political transition to end the conflict that began in March 2011 with peaceful democracy protests and turned violent following a brutal government crackdown.
The United States and Russia now agree Syria possesses about 1,000 metric tonnes of various chemical agents, including mustard and sarin gas, sulphur and VX.
US officials also said there were around 45 sites that inspectors would have to check and Kerry said it would be feasible to do that, despite the fighting.
UN chief Ban Ki-moon has accused Assad of multiple crimes against humanity and said a UN inspectors' report due to be published Monday would provide "overwhelming" confirmation chemical weapons were used on August 21.