An attack by IS suicide bombers on an air base hosting US marines in Iraq has been thwarted by the Iraqi army, the Pentagon said.

About 25 Islamic State fighters, led by several suicide bombers, attacked Ain al-Asad air base in Iraq's Western Anbar province.

The Pentagon said that the assault was thwarted, however, by Iraqi troops guarding the perimeter, with most of the assailants killed.

The sprawling air base is hosting US Marines training Iraqi military troops.

The base is close to the town of al-Baghdadi, which the Pentagon says is now under the control of Islamic State fighters after fierce fighting yesterday.

Rear Admiral John Kirby, the Pentagon press secretary, told reporters in Washington that US Marines were not involved in the fighting at the perimeter.

Drones and Apache helicopters were scrambled to assist but the fighting was over by the time they arrived, Army Colonel Steve Warren said.

Mr Kirby said some of the suicide bombers had detonated their vests.

"It does appear now that most, if not all of them, were wearing Iraqi uniforms," Mr Kirby said of the attackers.

An Iraqi official said Islamic State had been cleared from most of al-Baghdadi, with the remaining fighting centred around a police station.

That conflicted with reports from a tribal leader who said the jihadists were still in control of much of the town.

Mr Kirby said US assessments indicated Islamic State fighters were in control of al-Baghdadi.

Ongoing clashes and poor communications in the area made it difficult to confirm such reports.

Al-Baghdadi has been besieged for months by Islamic State, which captured swathes of northern and western Iraq last year.

About 320 US Marines are training members of the Iraqi 7th Division at the base.

The base has been struck by mortar fire on at least one previous occasion since December.

The US and its coalition partners conducted seven air strikes against IS militants in Iraq between early Thursday and early Friday.

Five of those were in the vicinity of Ain al-Asad base.