US Secretary of State John Kerry is in Moscow for talks on ways to bridge gaps over possible Syria peace talks.
Ahead of his meeting with his Russian counterpart Sergei Lavrov, Mr Kerry said he hoped to find common ground.
Later, he will meet President Vladimir Putin, as the two nations seek to narrow the gap on which groups should be included in the planned talks.
They also disagree on what role Syria’s President Bashar al-Assad should play in any transitional period.
The US wants him to stand down, but Russia says only the Syrian people should decide his fate.
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 Islamic State (IS), but activists say its strikes have mainly hit Western-backed rebel groups.
A US-led coalition has been targeting IS positions in Syria since September 2014 and does not co-ordinate its raids with the authorities in Damascus.
There has been some confusion (to put it mildly) about whether Russia is or isn’t supplying weapons and ammunition to the Free Syrian Army (FSA).
Last week, President Putin said it was – then, a few hours later, his spokesman Dmitry Peskov denied it.
On Monday, the chief of the Russian general staff said Russia was supporting the FSA with arms, ammunition and material help (copying Mr Putin almost word for word). But a few hours later a Kremlin aide denied that Moscow was supplying anything.
I used the Tuesday morning conference call with the Kremlin to try to get some clarity. Alas, I failed. This is what Mr Peskov said: “I have nothing to add to what’s already been said. I have nothing to add and I don’t want to explore this subject.” No harm in trying.