A Downing Street spokesperson said:
The Prime Minister, along with Chancellor Merkel, President Hollande, and Prime Minister Renzi, called President Putin this morning to discuss Syria.
The aim of the call was to give a clear, coordinated message on the importance of Russia and the Assad regime respecting the fragile truce to provide space for productive peace talks, due to resume in Geneva next week, and to allow humanitarian access to besieged Syrian towns.
The Prime Minister emphasised that it was in all our interests to defeat Daesh in Syria and, along with European leaders, he underlined the importance of recognising that the solution to the Syrian crisis lay in a transition away from Assad to a government that included moderate Sunnis which could reunite Syria and bring peace and stability to that country.
President Putin said that Russia was committed to ensuring that all sides respected the current truce and he agreed that we should all support the efforts of UN Special Envoy Steffan de Mistura to progress the negotiations in Geneva and move towards political transition.