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 people of Aleppo in Syria are going to take some convincing that a truce will actually happen.
Much of the city is in ruins after five years of fighting and President Bashar al-Assad is making rapid ground with his Russian-backed assault.
Many continue to flee the war-torn country, for whom any ceasefire would come too late.
ITV News Middle East Correspondent Geraint Vincent reports:
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.