The Russian and US foreign ministers have begun crucial talks in Geneva on a plan to place Syria's chemical weapons under international control.
Sergei Lavrov and John Kerry said they hoped the plan could avoid military action against Syria.
The UN has confirmed it has received documents from Syria on joining the Chemical Weapons Convention, a key step in the Russian plan. Syria's president said it would submit arms data one month after signing.
The US accuses the Syrian government of killing hundreds in a chemical attack in the Ghouta area of the capital, Damascus, on 21 August. The government denies the allegation, blaming rebels.
Russia announced its proposal for dealing with the escalating chemical weapons crisis on Monday, as the US Congress was preparing to debate whether to back President Barack Obama's moves towards military strikes.
'Doable but difficult'
In a news conference ahead of a working dinner in Geneva, Foreign Minister Lavrov said the resolution of the chemical weapons issue in Syria would make any military strike by the United States unnecessary.
He said there had to be a move away from military confrontation, and that successful talks could lead to a "Geneva 2" meeting.
Secretary of State Kerry said that only the threat of force had spurred Syria to accept relinquishing its chemical weapons, but that he hoped diplomacy could prevent military action.
He said the expectations for the meeting were high - particularly for Russia.
Mr Kerry said: "This is not a game... it has to be real, it has to be comprehensive, it has to be verifiable, it has to be credible, it has to be... implemented in a timely fashion... Finally, there ought to be consequences if it doesn't take place."
He added: "President Obama has made clear that should diplomacy fail, force might be necessary."
The Syrians' use of the phrase "standard practice" in supplying information to the UN appeared to irk Mr Kerry.
"There is nothing standard about this process at this moment because of the way the regime has behaved," he said.
Mr Lavrov appeared to admonish Mr Kerry for making a political address, saying: "Diplomacy likes silence". Mr Kerry failed to hear the translation of Mr Lavrov's final words and asked to hear them again.
Mr Lavrov said in English, "It's OK, John", only for Mr Kerry to say, smiling: "You want me to take your word for it - it's a little early for that."
The BBC's James Robbins, in Geneva, says these are critical talks, aimed at breaking two-and-a-half years of deadlock over Syria.
Our correspondent says the American and Russian teams are unusually large - packed with weapons experts as well as diplomats.