The head of Syria's main opposition coalition has been invited to Moscow after having his first direct talks with Russia's foreign minister.
Sergei Lavrov and Moaz al-Khatib, who leads Syrian National Coalition, met on the sidelines of an international security conference in Munich.
Moscow is a long-time ally of Syrian President Bashar al-Assad.
Later, Lavrov met US Vice-President Joe Biden and UN special envoy Lakhdar Brahimi.
Biden told it was "no secret" that Moscow and Washington had "serious differences" on issues such as Syria.