A Downing Street spokesperson said:
The Prime Minister spoke to President Obama earlier today ahead of the UN General Assembly in New York next week.
Their discussions focused on the situation in Syria. They agreed that the increasing number of refugees fleeing the country and the threat from ISIL underlined the need to make progress on political transition to end the Syria conflict.
They also talked about the opportunity of using UNGA to build support for an ambitious global agreement at the climate conference in Paris later in the year.