Russian Prime Minister Dmitry Medvedev has warned that sending more foreign ground troops into Syria will result in "a full-fledged, long war".
He hit back at the US Secretary of State John Kerry, who has suggested more countries could enter the conflict if diplomatic efforts fail to reach a solution.
The Russian PM has also said ongoing tensions between Russia and the West have plunged the world into "a new period of Cold War".
US Secretary of State John Kerry has accused Russia of hitting legitimate opposition groups and civilians with its bombing campaign in Syria.
Speaking at a security conference in Munich, Mr Kerry said Moscow must change its targets in order to respect a ceasefire deal agreed on Friday.
He also said Moscow had been dropping so-called "dumb bombs" that do not have a precise target, leading to the killing of civilians.
Earlier, Russian Prime Minister Dmitry Medvedev rejected claims Russia has bombed civilians in Syria, saying: "There is no evidence of our bombing civilians, even though everyone is accusing us of this."
Syrian President Bashar al-Assad has vowed to regain control of the entire country but warned it could "take a long time".
Marathon talks agree a partial ceasefire but fail to secure an end to Russian bombing, while rapid humanitarian aid won't reach all Syrians.