The service members’ identities were being withheld as family members were notified.

The deaths occurred as Iraqi counterterrorism forces, backed by American military advisers, carried out operations in a series of tunnels in the area. The Iraqi military released a statement saying that at least 25 Islamic State fighters were killed and that nine tunnels and a training camp were destroyed.

AD

AD

A senior U.S. official, speaking recently on the condition of anonymity because of the sensitivity of the issue, said that there are “small cells” of Islamic State fighters living in cave complexes, isolated from the Iraqi population.

"They’re trying to get some sort of resurgence, but they are disconnected,” the U.S. official said.

The militants are sustaining themselves through a mix of kidnapping and extortion from nearby communities, according to Iraqi security officials and residents in affected areas. In some cases, Islamic State fighters have collected ransoms of up to $70,000.

The militants “tend to work the seams,” the U.S. official said, referring to areas of disputed territory between the border of federal Iraq and the country’s Kurdish region, where security forces have been unable to establish any meaningful foothold, and the terrain favors insurgents.

AD

AD

Members of Marine Corps Forces Special Operations Command (MARSOC), known as Marine Raiders, have had an active role in counterterrorism operations in Iraq for years, teaming with Iraqi security forces to root out remnants of the Islamic State.

The last American service member killed in Iraq was Marine Gunnery Sgt. Scott A. Koppenhafer, a Raider who died in August during an operation in Iraq’s Nineveh province.