US and Russian negotiators remain at odds on a United Nations Security Council resolution that would hold Syria accountable if it fails to live up to pledges to dismantle its chemical weapons stockpiles.
Meanwhile, President Barack Obama warned the world body that it risked its credibility and reputation if it did not act.
US secretary of state John Kerry and Russian foreign minister Sergey Lavrov met for nearly 90 minutes and though progress was made in some areas, they were unable to reach agreement on the text of a resolution that would meet Mr Obama's standard, US officials said.
Mr Kerry told reporters after the meeting that the session had been "very constructive".
But three senior officials familiar with the effort say negotiations remain a work in progress as the US pushes for a binding, enforceable, verifiable arms-control regime that strips Syria of its entire chemical weapons stocks and facilities. The US is also demanding that the resolution contains no ambiguities or loopholes, they said.
The officials say several "key conceptual hurdles" are points of contention with the Russians as both sides seek agreement on the language of the resolution. The US and Russian ambassadors to the United Nations have been tasked with working out the language.
UN diplomats say differences between the US and Russia on how a resolution should be enforced have held up action in the security council. Russia is opposed to any mention of Chapter 7 of the UN Charter, which includes military and non-military actions to promote peace and security.
Russia and China have vetoed three Western-backed resolutions that would have pressured Syrian president Bashar Assad to end the two and a half-year war that, according to the UN, has killed more than 100,000 people.
Work on the resolution is going on at the same time as the Organisation for the Prohibition of Chemical Weapons, the body that will be in charge of securing and destroying the arms, is working on its own document to lay out its exact duties.
The two resolutions must be completed and agreed in tandem if the US-Russian agreement is to succeed, the US officials said.