Iraqi forces battling to retake Mosul have cut the last road out of the city, trapping Islamic State group fighters inside, the US envoy to the anti-IS coalition said Sunday.

"ISIS is trapped. Just last night, the 9th Iraqi army division, up near Badush, just northwest of Mosul, cut off the last road out of Mosul," Brett McGurk told journalists in Baghdad. "Any of the fighters who are left in Mosul, they're going to die there."