WASHINGTON (AFP) - US warplanes and drones carried out 15 air strikes on Monday against Islamic State (IS) militants battling for control of a major dam in northern Iraq, the military said.

Fighter jets, bombers and unmanned planes destroyed nine Islamic State positions and eight vehicles around the Mosul dam, where insurgents are fighting Kurdish forces, US Central Command said.

The US military launched a wave of air strikes in northern Iraq just over a week ago with the stated aim of protecting a group of Yazidi minority refugees and preventing an IS advance on the city of Arbil.

President Barack Obama said last week that the siege of the Yazidi civilians has been broken, but strikes have only intensified as US-backed Kurdish and Iraqi forces try to secure the key dam.

"Since Aug 8, US Central Command has conducted a total of 68 airstrikes in Iraq. Of those 68 strikes, 35 have been in support of Iraqi forces near the Mosul Dam," the statement said.

Monday's barrage destroyed nine IS fighting positions and a checkpoint, six armed trucks, an armored vehicle, a mobile anti-aircraft gun and a patch of ground booby-trapped with improvised explosives.

Central Command said the strikes had been conducted under the authority of Mr Obama's order to support Iraqi and Kurdish forces in the fight against IS militants and to protect US personnel and facilities.