Washington is not prepared to trust the word of the Syrian regime alone that it will rid itself of chemical weapons, US Secretary of State John Kerry said Thursday.

"The words of the Syrian regime in our judgement are simply not enough, which is why we've come here in order to work with the Russians," Kerry told reporters in Geneva ahead of high-stakes talks with his Russian counterpart Sergei Lavrov on the thorny issue of Syria's chemical weapons.

He warned it was also up to Russians to show that they could "deliver on the promise of the moment" after Moscow proposed a plan earlier this week to eliminate Syria's deadly weapons stock.

But Kerry highlighted that the US and Russia still disagreed on who carried out a suspected sarin gas attack near Damascus last month, which Washington says killed 1,400 people.

The attack came in the midst of a brutal civil war which began as a popular uprising to topple President Bashar al-Assad, and which is said to have cost some 110,000 lives in about two and a half years.

"The Russian delegation has put some ideas forward and we're grateful for that. We respect it. And we have prepared our own principles that any plan to accomplish this needs to encompass," Kerry stressed, before a room packed with reporters from around the world.

"Expectations are high. They are high for the United States, perhaps even more so for Russia to deliver on the promise of this moment. This is not a game," he said.

Any deal to bring Syria's chemical weapons stockpile under international control "has to be credible. It has to be timely and implemented in a timely fashion," he said.

Kerry and Lavrov, who have both brought a team of top-level weapons experts with them to pore over the details of the Russian plan, will be making a posh Geneva hotel their operating base until Saturday for the closed-door talks.

The top US diplomat told Lavrov that the United States was "serious as you are, engaging in substantive meaningful negotiations".

"Despite how difficult this is, with the collaboration of our experts, and only with the compliance from the Assad regime, we do believe there is a way to get this done," he said.

"Together we will test the Assad regime's commitment to follow through on its promises".

Lavrov, who addressed the press first, said: "The solution of this problem makes unnecessary any strikes on Syria".

Pending the talks, US President Barack Obama has put on hold plans for limited military strikes against the Syrian regime to disable its chemical weapons capability.

"I am sure that our American partners... are strongly in favour of a peaceful way to regulate chemical weapons in Syria," Lavrov said.

He also told Kerry, speaking through a translator, that "I hope we will achieve all the successes".

But Kerry quipped: "You want me to take your word for it? It's a little early for that".