US warplanes and drones carried out 15 air strikes against Islamic State 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.

Earlier, Kurdish peshmerga fighters and Iraqi counter-terrorism forces were reported to have pushed IS militants away from the dam.

Iraqi state television station quoted military spokesman Lieutenant-General Qasim Atta as saying the forces were backed by a joint air patrol.

He did not give details.

An independent verification was not immediately possible.

A Twitter account belonging to a media organisation that supports the IS said the dam was still under the group's full control.

Yesterday, a Mosul dam engineer who has been in close contact with IS militants holding the dam, said they had placed bombs along roads leading in and out of the complex in anticipation of an assault.

The latest northern Iraq offensive by IS militants has rattled the Baghdad government and its Western allies, prompting the US to mount the first air strikes in the country since it withdrew in 2011. 

Militants have seized several towns and oil fields as well as the Mosul dam in recent weeks, possibly giving them the ability to flood cities or cut off water and electricity supplies.

Asked about a Kurdish push to dislodge the Sunni fundamentalist militants yesterday, a Kurdish official said the dam had not been retaken but "most of the surrounding area" had been seized.

The US said it conducted 14 air strikes yesterday against Islamic State fighters near the dam.

US Central Command said the latest strikes destroyed three armed vehicles, a vehicle-mounted anti-aircraft and an emplacement of the IS as well as one of the militants' checkpoints.

The strikes followed nine US air strikes on Saturday near the dam and the Kurdish capital, Irbil.

Meanwhile, US President Barack Obama has said that the United States has embarked on a long-term mission to defeat the insurgents of the so-called "Islamic State" fighting in Iraq.

Ten days after ordering air strikes against the jihadist fighters, Obama warned that IS remains a threat to Iraq and the wider region, telling Baghdad "the wolf is at the door."