A U.S. service member died Thursday from wounds sustained in an improvised explosive device blast in northern Iraq, the U.S. military said.

The U.S. military did not release details. American advisers are with Iraqi forces in the battle for Mosul, the largest offensive yet against the Islamic State in Iraq. The serviceman was part of the Mosul operation, said a U.S. official who asked not to be named because he was not authorized to discuss the incident publicly.

On Monday, Iraqi forces launched a major offensive to retake Mosul — Iraq's second-largest city — from Islamic State control. American advisers are generally positioned with headquarters and are not engaged in direct combat.

Still, U.S. officials cautioned that the troops are still exposed to danger. "Americans are in harm's way as part of this fight," Pentagon Press Secretary Peter Cook said earlier this week.

It is the fourth U.S. combat death since U.S. troops deployed in 2014 to support Iraq's military in the fight against the Islamic State. Last year, Master Sgt. Joshua Wheeler, 39, was killed during a raid on an Islamic State prison compound.

In March, Marine Staff Sgt. Louis Cardin, 27, died when Islamic State militants attacked a firebase about 60 miles south of Mosul. In May, a Navy SEAL, Special Warfare Operator 1st Class Charles Keating IV, 31, was killed in a firefight after his quick reaction force came to aid an advisory team whose base was under attack by militants.

There are about 5,000 U.S. troops in Iraq, mostly conducting advisory and training missions. About 100 U.S. troops are embedded with Iraqi units engaged in the Mosul operation.