US Secretary of State John Kerry is holding talks with Russian President Vladimir Putin in Moscow on Tuesday to discuss the crisis in Syria, reports say.
According to AFP, US officials said on Monday that both sides are "ready to engage on Syria".
Kerry's visit comes after Israel launched two air strikes in southern Syria,  which sources say targeted weapons bound for Lebanon's Hezbollah. Russia condemned the attacks as threatening regional stability.
On Monday, UN investigator Carla Del Ponte said testimony from victims and doctors had given rise to "strong, concrete suspicions but not yet incontrovertible proof" that Syrian opposition forces had used the nerve agent sarin. 
The US has previously said that the use of chemical weapons in the Syrian conflict would be a 'game-changer', which could trigger military intervention.