The United States and Russia yesterday agreed on an ambitious plan to eliminate Syria's chemical weapons by the middle of next year.
In a landmark deal thrashed out in talks spanning three days, the two powers gave Syrian President Bashar al-Assad a week to hand over details of his regime's stockpile.
US Secretary of State John Kerry said Assad's regime must also provide "immediate and unfettered" access to inspectors from the Organisation for the Prohibition of Chemical Weapons.
"The inspectors must be on the ground no later than November ... and the goal is to establish the removal by halfway through next year," Kerry said alongside Russian Foreign Minister Sergei Lavrov.
US President Barack Obama welcomed the deal but said much remained to be done and Damascus must comply with the accord.
Obama said that if the regime of Assad did not live up to the deal, "the United States remains prepared to act".
Kerry said the steps agreed to yesterday would be encapsulated in a UN Security Council resolution drawn up under Chapter Seven of the organisation's 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 and wielding a veto on the Security Council, Kerry acknowledged it was "impossible to have a pre-agreement" on what would happen in the event of non-compliance.
Lavrov signalled that Moscow would back some form of sanction, saying that the Security Council would act under Chapter Seven if Syria failed to meet its demands.
Lavrov hailed yesterday's accord as an "excellent" agreement "whose significance is hard to overestimate".
The accord was greeted with dismay by the Syrian opposition coalition, which has spent two years appealing to the West to give it the weapons needed to tilt the balance of the civil war in their favour. "We cannot accept any part of this initiative," said General Selim Idriss, the head of the Free Syrian Army.
Washington and Moscow hope to revive plans for peace talks in Geneva that would bring together Assad's regime and the opposition to agree a political transition to end the war that erupted in March 2011.
Kerry and Lavrov will meet again in a few weeks on the sidelines of the UN General Assembly in New York, with the hope of setting a date for the stalled peace conference.
France welcomed the Geneva deal. "The plan is a significant step forward," Foreign Minister Laurent Fabius said.
The United States has estimated that Syria possesses around 1,000 metric tonnes of various chemical agents, including mustard and sarin gas.
Russian estimates had been much lower but Kerry said that the two countries had reconciled their assessments.