"F-16s first entered Iraqi airspace on a reconnaissance mission and are now targeting Daash (Islamic State) in Gwer and in the Sinjar region," Holgard Hekmat told AFP.

Pentagon spokesman Rear Admiral John Kirby said that reports of US airstrikes were false. "No such action taken," he said on Twitter.

The Kurdish official said: "They just struck the bridge linking Mosul to Gwer. The bridge had been used by Daash to channel reinforcements and ammunition to Gwer."

He added: "Their main supply line is now cut, they are isolated in Gwer and the F-16s are striking them there." Hekmat did not elaborate on the targets in the Sinjar area, further west.

Gwer lies just 30 kilometres (20 miles) southeast of the main checkpoint leading to the autonomous Kurdistan region.

A series of jihadist attacks in that area and further east in the Sinjar area near the Syrian border has displaced tens of thousands of civilians in recent days.