Two U.S. service members were killed in Iraq Sunday while advising Iraqi Security Forces on a mission against ISIS, U.S. officials confirmed Monday.

The U.S. and Iraqi forces were on a “mission to eliminate an ISIS terrorist stronghold in a mountainous area of north central Iraq,” said a statement from Combined Joint Task Force – Operation Inherent Resolve.

“On the evening of March 8, the U.S.-led Coalition launched additional forces to recover two U.S. service members from the southern Makhmur Mountains in Iraq, approximately 60 km south of Erbil,” Col. Myles B. Caggins III, coalition military spokesman, told Marine Corps Times Monday.

It took coalition forces six hours to recover the killed Marines, Caggins said.

A source familiar with the operation told Marine Corps Times on background that the Americans were Marine Raiders partnering with Iraqi special forces in a large operation against ISIS.

The names of those killed are being withheld until next-of-kin can be notified.

Pentagon identifies Marine Raider killed in Iraq Gunnery Sergeant Scott A. Koppenhafer, 35, of Mancos, Colorado, died August 10, 2019, after being engaged by enemy small arms fire while advising and accompanying Iraqi security forces on a planned operation in Ninewah, Province, Iraq. This incident is under investigation.

Throughout the past two weeks, official Iraqi government Twitter accounts have been posting about fights in the Hamrin and Makhoul mountain ranges in northern Iraq.

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Early Monday morning the Iraq media security cell tweeted about a clash between Iraqi special operations anti-terror forces and terrorists that killed several terrorists in tunnels discovered in the Makhoul mountains.

“The purpose of the mission was to eliminate ISIS safe-havens in a cave complex in the Makhmur Mountains,” Caggins said.

“The Makhmur Mountains are historically known to be an ISIS safe haven. However, there is no safe place for ISIS to hide,” he added.

The military currently estimates that between 17–19 ISIS fighters were killed in the attack.

The two service members killed are the first combat deaths as part of Operation Inherent Resolve since Marine Raider, Gunnery Sgt. Scott A. Koppenhafer, 35, of Mancos, Colorado, was killed in August 2019.

Koppenhafer died in Ninewah province, Iraq, while advising Iraqi forces in its fight against the Islamic State, Marine Corps Times previously reported.

Inherent Resolve is a multinational operation tasked with defeating ISIS in Iraq in Syria.

Since the operation began in 2014, 17 U.S. service members have been killed in action, according to the Defense Casualty Analysis System.

The two new deaths bring the total to 19 troops killed.

“The Coalition, alongside our partner forces, will continue to hunt the remnants of the illegitimate caliphate in order to disrupt any effort to resurge,” Caggins said.

This is a breaking story and will be updated as Marine Corps Times confirms more.

Overseas operations reporter Shawn Snow contributed to this report.