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".
Tensions between Russia and the West have plunged the world into a "new Cold War", Dmitry Medvedev has said.
The Russian Prime Minister said his country was "accused of making new horrible threats either against NATO as a whole, against Europe or against the US or other countries" on an almost daily basis.
Relations between Russia and the West have been strained by the Ukraine conflict and Russia's backing of Bashar al-Assad's regime in Syria.
Speaking at the Munich Security Conference, Mr Medvedev said: "We can say it even more clearly: We have slid into a new period of Cold War."
He said the US and Russia needed to cooperate regularly to resolve the crisis in Syria.
Mr Medvedev also rejected claims Russia has bombed civilians in Syria, saying there was "no evidence" to back the accusations.
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.