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".
Philip Hammond appeared to be unimpressed with Russia's response to the accusations that the country's forces have bombed civilians, rolling his eyes as Russian Foreign Minister Sergei Lavrov defended his country's actions.
The Foreign Secretary shook his head and looked to the sky as Lavrov spoke at a security conference in Munich about how "moving closer to practical goals of truce" would not work without co-operation between military forces.
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.