“I think De Mistura is fooling himself if he thinks that Assad is part of the solution,” coalition member Samir Nashar told AFP by telephone from Istanbul.

“Assad is the problem, not part of the solution.”

Najib Ghadbian, the National Coalition’s UN envoy, described the “brutality” of Assad’s regime as the root cause of the conflict.

He also warned the US-led alliance fighting the Islamic State group – which has seized swathes of territory in both Syria and Iraq – that its efforts would fail unless world powers get serious about a peace plan for Syria.