Russian Foreign Minister Sergei Lavrov has said neither side can win the war in Syria, and that China and Russia would be unable to persuade President Bashar al-Assad to quit if they tried.

Russia has been backtracking since the Kremlin's Middle East envoy was quoted this month as saying the rebels could defeat Mr Assad and that Russia was preparing for a possible evacuation of its nationals.

It was seen as the strongest sign yet that it was positioning itself for a post-Assad Syria.

"Listen, no one is going to win this war," Mr Lavrov told reporters aboard a government plane en route to Moscow after a Russia-European Union summit in Brussels.

Russia has angered the West and some Arab states by vetoing, along with China, three UN Security Council resolutions meant to put pressure on Mr Assad to end the bloodshed.

More than 40,000 people have died since his government began a crackdown on protests in March 2011.

Russia contends it is not trying to prop Mr Assad up, but Mr Lavrov reiterated that it has no intention of helping remove him - and said it anyway lacks the influence to make that happen.

"Assad is not going anywhere, no matter what anyone tells him, be it China or Russia," he said.

"Some regional powers suggested that we tell Assad we were ready to accommodate him. And we replied: 'Why do we have to do it? If you have these plans, go to him directly yourselves'."

Mr Lavrov suggested Russia would not object "if there are those who are ready to give him some guarantees, if this stops the bloodshed - but only if it could stop the bloodshed, which does not seem to be a clear fact".

"Western intelligence services have serious fears and forecasts that the toppling of Assad would not resolve the problem, that fighting would move to a new stage," he said.

Russian President Vladimir Putin said on Thursday that Russia was not concerned about Syria's current rulers staying in power but feared the government and its opponents might simply swap roles and fight on forever.

If "the number one priority is to end bloodshed and save lives, we need to simply put the 'Assad problem' aside," Mr Lavrov said.

"And make everyone declare a truce, bring in UN observers, and sit the warring parties at the negotiation table without preliminary terms like the resignation of Syria's president."

He said international envoy Lakhdar Brahimi would visit Russia before the end of the year.

Mr Brahimi has twice this month met with Russian and US diplomats but the talks produced no signs of progress in ending their disagreements over Syria.

Russia says the solution must be based on a deal reached in Geneva in June that called for a transitional government.

US Secretary of State Hillary Clinton said at the time that the declaration made clear Mr Assad should step down, but Mr Lavrov said it did nothing of the kind.

In his latest remarks, Mr Lavrov suggested that, by supporting rebels, Western countries were undermining their own goal of ensuring Syria's chemical weapons are not used.

"In our confidential conversations, our US partners acknowledge that the main threat [connected to chemical weapons] is their capture by rebels," he said.

"We tell them: 'Guys, but you are supporting the opposition and its armed resistance'."

Mr Lavrov said that, for now, the chemical arsenal was "under control", adding: "The Syrian authorities have concentrated those reserves, previously scattered across the country, in one or two centres."

He did not say when that had taken place or give any details.

US Defence Secretary Leon Panetta expressed concern this month that Mr Assad's government was considering using chemical weapons as rebels intensified their push, but he said on 11 December that there had been no new moves in recent days indicating that.