The US and Russia say world powers will meet in New York on Friday to pass a UN resolution endorsing the Syria peace process.
It follows talks in Moscow between US Secretary of State John Kerry, his Russian counterpart Sergei Lavrov and President Vladimir Putin.
Russia launched an air campaign to bolster Mr Assad's government in September. It says it has targeted only "terrorists", above all jihadist militants from the Islamic State (IS) group, but activists say its strikes have mainly hit Western-backed rebel groups.
Friday's meeting in New York would pass a UN resolution reaffirming the principles of the peace process agreed in Vienna last month.
Mr Kerry travelled to Moscow to try to bridge gaps over ways to end the Syrian conflict.
The US and Russia disagree on what role Syrian President Bashar al-Assad should play in any transition.
The US wants him to stand down, but Russia says only the Syrian people should decide his fate.