Syria's chemical weapons must be destroyed or removed by mid-2014, under an agreement between the US and Russia.
US Secretary of State John Kerry outlined a framework document under which Syria must hand over a full list of its stockpile within a week.
If Syria fails to comply, the deal could be enforced by a UN resolution backed by the threat of sanctions or military force.
The US says the Syrian regime killed hundreds in a gas attack last month.
The government of Bashar al-Assad denies the allegations and has accused the rebels of carrying out the attack on 21 August.
Syria recently agreed to join the global Chemical Weapons Convention, and on Saturday the UN said it would come under the treaty from 14 October.
In a joint news conference with Russian Foreign Minister Sergei Lavrov, Mr Kerry called on the Assad government to live up to its public commitments.
"There can be no room for games, or anything less than full compliance by the Assad regime," he said.
Mr Kerry and Mr Lavrov said if Syria failed to comply, then a UN resolution would be sought under Chapter VII of the UN charter, which allows for the use of force.
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 regime hands, half of which have useable quantities of chemical agents, the official added.
However, it is thought that Russians have not agreed the number of sites, nor that they are all under control.
The agreement says initial on-site inspections must be complete by November.
It also stipulates that production equipment be destroyed by November, with "complete elimination of all chemical weapons material and equipment in the first half of 2014".
Mr Kerry outlined six points to the agreement:
- The amount and type of chemical weapons must be agreed and "rapidly" placed under international control
- Syria must submit within one week a comprehensive listing of its stockpiles
- Extraordinary procedures under the Chemical Weapons Convention will allow "expeditious destruction"
- Syria must give inspectors "immediate, unfettered access" to all sites
- All chemical weapons must be destroyed, including the possibility of removing weapons from Syrian territory
- UN will provide logistical support, and compliance would be enforced under Chapter VII
The White House described the deal as "an important concrete step" towards putting Syria's chemical weapons under international control.
However, it warned that "if diplomacy fails, the United States remains prepared to act".
France and the UK both welcomed the agreement.
French Foreign Minister Laurent Fabius said it was an "important advance". France was the only country willing to join the US in taking military action in Syria.
British Foreign Secretary William Hague said in a statement: "The onus is now on the Assad regime to comply with this agreement in full. The international community, including Russia, must hold the regime to account."
UN Secretary-General Ban Ki-moon said he pledged "the support of the United Nations in its implementation".
Nato Secretary General Anders Fogh Rasmussen also welcomed the deal, saying it was an "important step towards the goal of ensuring the swift, secure and verifiable elimination of Syria's stocks of chemical weapons".
However, the military leader of the anti-Assad Free Syrian Army 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.
Not all American politicians welcomed the deal either. Republican senators John McCain and Lindsay Graham said it would give President al-Assad months to "delay and deceive".
"It requires a wilful suspension of disbelief to see this agreement as anything other than the start of a diplomatic blind alley," they said in a statement.
Meanwhile, on the ground in Syria:
- Fighting continued on Saturday. Activists reported clashes between government forces and rebels in suburbs of Damascus, including some of the same areas affected by the 21 August attack.
- The main Western-backed opposition group, the Syrian National Coalition, has elected a long-term political activist, Ahmad Saleh Touma, as interim prime minister. The group is seeking to become a viable political alternative to Bashar al-Assad's regime.
- Video footage has emerged of an interview from a now-deceased Iranian commander apparently working with government forces. "Many of our Syrian friends here find it easy to work with us, because many of them have been trained by us in Iran," he said.
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 in the past 24 hours.
Millions more have been internally displaced within Syria.