Russia was forced to deny that it was close to major policy shift on Friday after France alleged that the Kremlin had discussed a post-Assad Syria.
Laurent Fabius, the new French foreign minister, claimed that negotiations were under way to persuade Moscow to abandon its crucial support for President Bashar al-Assad, suggesting that the only sticking point was over who should succeed him.
"The Russians are not today attached to the person of Bashar al-Assad," said Mr Fabius. "They clearly see he is a tyrant and a murderer. But they are sensitive about who might take his place if Assad is ousted. The discussion is about that."
Mr Fabius's comments appeared to be part of a concerted diplomatic effort to prise Russia apart from Mr Assad's regime.
Faced with a sharp escalation of the Syrian conflict following two recent civilian massacres in recent weeks, Western states have visibly stepped up pressure on Moscow to convince it of the need for regime change.
But Sergei Lavrov, the Russian foreign minister, curtly rebuffed suggestions of a change of heart, denying that any negotiations with the West about Mr Assad's departure were under way.
"There were no such discussions and there could not be such discussions," he said. "We do not get involved in overthrowing regimes – neither through approval of unilateral actions by the UN Security Council nor by any participation in any political plots."
Despite Moscow's public protestations, Western states remain convinced that Russia can be won round. Several officials said that Russia would accept his departure if the Syrian people called for it, prompting Hillary Clinton to dispatch a number of envoys to Moscow in the hope of persuading it to back a new peace plan that would be centred on Mr Assad's resignation.
Desperate to maintain a vital strategic relationship with its most important Arab ally, however, Russia has persistently vetoed Western efforts to impose sanctions on the Assad regime and has been instrumental in ensuring the Syrian president's survival.
Amid heightened international urgency over how to respond to the worsening crisis, the head of the UN observer team admitted that the peace plan which established his mission was fast disintegrating.
"Violence over the past 10 days has been intensifying, again willingly by both parties, with losses on both sides and at significant risk to our observers," said Major-General Robert Mood.
"The escalating violence is now limiting our ability to observe, verify, report as well as assist in local dialogue and stability projects."
Clashes were reported across Syria yesterday as regime forces stepped up an offensive to drive rebel forces out of their strongholds.