Russian and US diplomats are meeting on Sunday with UN peace envoy Lakhdar Brahimi for more talks on the civil war in Syria, Russian Foreign Minister Sergey Lavrov has said.

Russia agreed to take part in the talks in Geneva, Switzerland, he said, on the condition there would be no demand for Syrian president Bashar Assad to step down.

"We are not conducting any negotiations on the fate of Assad," Mr Lavrov said.

"All attempts to portray things differently are unscrupulous, even for diplomats of those countries which are known to try to distort the facts in their favour."

Mr Lavrov met last week with Mr Brahimi and US Secretary of State Hillary Rodham Clinton in Dublin.

Afterwards, Mrs Clinton said the US and Russia were committed to trying again to get both sides in the Syrian conflict to talk about a political transition.

She stressed that the US would continue to insist that Mr Assad's departure be a key part of that transition.

Russia and the US have argued bitterly over how to address the conflict, which began with peaceful protests against Mr Assad in March 2011 and escalated into a civil war.

The US has criticised Russia for shielding its closest ally in the Middle East while Moscow has accused Washington of encouraging the rebels and being intent on regime change.

Russia's foreign minister said on Sunday that after he agreed to a US proposal to have his and Mrs Clinton's deputies "brainstorm" on Syria, the Americans began to suggest that Russia was softening its position.

"No such thing," Mr Lavrov said. "We have not changed our position."

Germany weighed in on Sunday on the future of Mr Assad's regime, with Federal Intelligence Service chief Gerhard Schindler saying it would not survive, although it was impossible to say how long it would hang on.

"Signs are increasing that the regime in Damascus is in its final phase," he was quoted as telling the Frankfurter Allgemeine Sonntagszeitung.