UN and Arab League special envoy Kofi Annan has proposed setting up a transitional government in Syria, which would include representatives of Assad's government and opposition groups. Syria's key ally Russia has rejected the idea.
The international mediator's plan to end the 16-month conflict in Syria is expected to set the tone at the upcoming meeting of foreign ministers in Geneva.
The major powers are likely to back the plan, except for Russia, which is seeking amendments to the proposal.
Although Russia initially supported Annan's proposal to form a national unity government, Moscow is against President Bashar al-Assad being removed from power.
Russian foreign minister Sergei Lavrov hit out at a draft of the proposal being leaked to the media. "Any leaks to press from draft report on Annan plan are evidence of unscrupulous diplomatic practices," Reuters quoted Lavrov as saying.
Even though Annan's proposal did not explicitly indicate Assad's removal, it implies that certain people be removed from government, which Moscow has interpreted as referring to Assad.
Reuters reported western diplomats as saying on condition of anonymity that they supported Annan's plan.
Russia wants the idea of certain people from the regime being removed rom power to be deleted from the proposal, but it would be rejected by western nations.
Reports suggest the imbroglio between Russia and the west casts a shadow over the Geneva meeting.
Annan's proposal called for both sides in the conflict to immediately lay down their weapons to end the bloodshed. This was also reportedly contested by Moscow.
Western diplomats were quoted by Reuters as sharply criticising Russia's stand, saying the government should make the first move to disarm.
Ministers from the United States, the UK, France, Russia, China, Turkey and other Middle East countries are expected to attend the meeting in Geneva.
China will keenly watched, since it often takes Russia's lead on issues related to Syria.