US President Barack Obama has warned of "consequences" if the Syrian regime fails to comply with a framework deal to destroy its chemical weapons.
A framework document agreed by the US and Russia on Saturday stipulates that Syria must provide full details of its stockpile within a week.
The chemical arsenal must then be eliminated by mid-2014.
If Syria fails to comply, the deal could be enforced by a UN resolution with the use of force as a last resort.
But US officials say the president reserves the right to act without the agreement of the UN.
China, France, the UK, the UN and Nato have all expressed satisfaction at the agreement.
In Beijing, Foreign Minister Wang Yi said on Sunday that China the deal "will enable tensions in Syria to be eased".
There has so far been no reaction from Damascus.
Mr Obama said in a statement that the deal was an "important step" but urged Syria to "live up to its public commitments".
"If diplomacy fails, the United States remains prepared to act," he said.
The Pentagon said the US military was still in position for military strikes.
The US says the Syrian regime killed hundreds in a poison-gas attack in eastern Damascus on 21 August.
President Bashar al-Assad's government denies the allegations and has accused the rebels of carrying out the attack.
Syria recently agreed to join the global Chemical Weapons Convention, and the UN said it would come under the treaty from 14 October.
The framework deal was unveiled by Russian Foreign Minister Sergei Lavrov and US Secretary of State John Kerry in a news conference in Geneva.
Mr Kerry outlined a timetable that analysts said was extremely ambitious.
It envisages Syria providing a full inventory of its chemical weapons in one week, all production equipment being destroyed by November, and all weapons being removed from Syria or destroyed by mid-2014.
Both men confirmed that a UN resolution could be sought under Chapter VII of the UN charter, which allows for the use of force, if Syria fails to comply.
However the Russian foreign minister said force remained a last-ditch option.
"Naturally, no use of force is mentioned in these agreed approaches. Nor are any automatic sanctions mentioned. Any violations must be convincingly and unambiguously proven in the UN Security Council," he said.
Russia and the US have agreed on an assessment that the Syrian government possesses 1,000 tonnes of chemical agents and precursors, according to a US official.
The US believes the materials are located in 45 sites, all in government hands, half of which have useable quantities of chemical agents.
But it is thought that Russia does not agree on the number of sites, nor that they are all under the government's control.
French Foreign Minister Laurent Fabius, who is visiting Beijing, said it was an "important advance" while British Foreign Secretary William Hague said in a statement: "The onus is now on the Assad regime to comply with this agreement in full.
Analysts however remain divided.
Former British ambassador to Syria Sir Andrew Green said it was "remarkably good news" because it avoided military action, removed the risk of chemical attacks and generated dialogue with Russia.
But former US Deputy Secretary of Defence Paul Wolfowitz disagreed, saying the deal had "taken off the table" any serious threat of action against the Assad regime.
The military leader of the anti-Assad Free Syrian Army has rejected the deal and promised to continue fighting.
"There is nothing in this agreement that concerns us," said Gen Salim Idriss, describing it as a Russian initiative designed to gain time for the Syrian government.
Mr Kerry is due in Israel on Sunday to meet Prime Minister Benjamin Netanyahu and will then go to Paris to meet his French, British and Saudi counterparts.
Meanwhile there has been more fighting on the ground in Syria with clashes between government forces and rebels in the suburbs of Damascus, including some of the same areas affected by the 21 August attack.
More than 100,000 people have died since the uprising against President Assad began in 2011.
Millions of Syrians have fled the country, mostly to neighbouring nations. However, on Saturday, Italy's coastguard said more than 500 people, mostly Syrians, had been rescued off the Italian coast.
Millions more have been internally displaced within Syria.