An attack by ISIS terrorists on an air base hosting US Marines in Iraq has been defeated by the Iraqi army, the Pentagon has said.

About 25 ISSI militants, led by several suicide bombers, attacked Ain al Asad air base in Iraq's western Anbar province, Sky news reports.

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

The sprawling air base is hosting more than 300 US Marines training Iraqi troops.

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

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

Drones and Apache helicopters were scrambled but the fighting was over by the time they arrived.

US Army soldiers training Iraqi troops at the Taji base, north of Baghdad (AFP Photo)

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

He added US assessments indicated ISIS fighters were in control of al-Baghdadi. However, ongoing fighting and poor communications in the area made it difficult to confirm such reports.

Al-Baghdadi has been besieged for months by ISIS, which captured large areas of northern and western Iraq last year.

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

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

The US and its coalition partners carried out seven air strikes against ISIS militants in Iraq between early Thursday and early Friday.Five of those were in the vicinity of the base.