The UN envoy for Syria on Tuesday called the fight against militants in Syria a game changer, and said US air strikes could even help ease humanitarian needs.

The UN envoy for Syria on Tuesday called the fight against militants in Syria a game changer, and said US air strikes could even help ease humanitarian needs.

"In order to move at the moment there is obviously a game changer and the game changer is Daesh and the fight against Daesh," Staffan de Mistura told reporters at UN headquarters, using the Arabic acronym for the so-called 'Islamic State of Iraq and the Levant' (ISIL) group.

He said the current period was "delicate" and "dangerous" but that the priority was to care for the 11 million Syrians desperately in need of aid despite the welter of crises facing the world.

Asked if US air strikes would exacerbate the situation on the ground, de Mistura said he had no indication so far that the air campaign was affecting humanitarian assistance.

"On the contrary, I think that if there was any kind of reduction of the pressure by Daesh on the local population, we'll have less, a little bit, moving across (the border) and therefore less of an urgent need of humanitarian assistance."

De Mistura also spoke with some confidence about a forthcoming visit to Iran, a key player in the region and ally of the regime in Damascus.

"I think that Iran is an important player, and I hope an important partner in what should be a political process," he said.