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".
The distribution of humanitarian aid to war-torn Syria could begin as soon as Saturday if aid workers can gain access to besieged areas, UN spokesperson Ahmad Fawzi has said.
World powers agreed to establish a "cessation" of hostilities within a week after marathon talks in Munich, though Russian bombing raids will continue.
Mr Fawzi said representatives of the nations that met in Germany will convene for an afternoon meeting in Geneva to continue to discuss the humanitarian issue, which could speed up action as aid workers await access to begin the distribution.
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.