Two American soldiers fighting the Islamic State group in Iraq were killed during an operation alongside Iraqi forces, the coalition against the jihadists said Monday.

"Two U.S. service members were killed by enemy forces... during a mission to eliminate an ISIS terrorist stronghold in a mountainous area of north central Iraq, March 8," the coalition said in a statement, using an alternative acronym for the jihadist group.

It did not name those killed, but said they had been "advising and accompanying Iraqi Security Forces".

The US-led coalition has provided training and air support for Iraqi forces since 2014, after IS seized much of northern Iraq and large parts of Syria in a sweeping offensive.

The group had declared a "caliphate" and imposed a brutal form of Islamic law.

Iraqi forces backed by the coalition drove the jihadists from all urban centres in a gruelling battle, declaring victory in December 2017.

Coalition forces have since focused on conducting air strikes and surveillance to rout jihadist sleeper cells.

But the United States in January outraged Iraqi leaders by killing top Iranian general Qasem Soleimani in a drone strike at Baghdad airport -- an attack widely seen as a violation of Iraq's sovereignty that sparked demands for US forces to leave.

Iraq's parliament voted to oust all foreign troops from the country and joint Iraqi-coalition operations were paused for three weeks before resuming in late January.

Tensions had also soared as Iranian-linked Iraqi Shiite paramilitaries repeatedly fired rockets at bases hosting US forces.