麻豆约拍

Mouin Rabbani, a former senior adviser to the UN's Syria envoy, said David Cameron's claim that 70,000 rebels would fight IS "rests on a fundamental misconception".

He said the priority of these groups, who have been fighting the Assad regime and each other, is to seize Damascus rather than Raqqa.

Mr Rabbani, who was head of political affairs to Staffan de Mistura, resigned in frustration at the glacial rate of progress in January.