Syrian groups backed by the West have been accused of driving people into the arms of Isil, executing prisoners and killing hundreds of people in recent inter-factional fighting.

The YPG, the Kurdish group being backed both by the United States to fight Islamic State of Iraq and the Levant and by the Russians to fight US-supported anti-Assad rebels, is sending civilians into flight with its behaviour, according to a former US ambassador to the country, Robert Ford.

“In some cases, Syrian refugees flee it and don't go towards the Kurdish areas - they run away from them and into Islamic State territory,” Mr Ford told a Senate committee hearing.

He made the accusation at a time when both pro- and anti-regime forces in Syria are fragmenting under the pressure of the seemingly endless conflict.