Capt. Moises A. Navas, left, and Gunnery Sgt. Diego D. Pongo were killed in Iraq on March 8, 2020. (U.S. Marine Corps)

A Marine special operations captain and gunnery sergeant were both killed Sunday during a joint U.S.-Iraq raid to destroy an Islamic State hideout in a mountainous area in northern Iraq, the military said Tuesday.

Gunnery Sgt. Diego D. Pongo, of Simi Valley, Calif., and Capt. Moises A. Navas, of Germantown, Md., both 34 and both with 2nd Marine Raider Battalion out of Camp Lejeune, N.C., were identified in a Pentagon statement as the two Americans killed by enemy forces.

The pair were supporting Iraqi security forces during the operation, the U.S.-led Combined Joint Task Force-Operation Inherent Resolve said in a statement earlier in the week.

Pongo, who joined the Marines in 2004 and served eight years with the elite Marine Raiders, is survived by his daughter and his mother, Marine Forces Special Operations Command said in a statement.

“They were intelligent, courageous and loyal,” said Col. John Lynch, head of Marine Raider Regiment. “They were dedicated leaders, true professionals in their craft, and willing to go above and beyond for the mission and their team. They were also family men, adoring husbands and fathers.”

Navas, who previously served as an enlisted Marine after joining in 2004, earned his commission through an enlisted-to-officer program in 2010 and served as an infantry officer before becoming a Raider in 2016. He is survived by his wife, daughter and three sons.

U.S. officials have released few official details about the operation in which the two were killed and the Pentagon said the incident is under investigation, but the Iraqi government said online Monday that its elite forces, aided by coalition aircraft, had carried out an air assault on a mountain near the Iraqi town of Makhmour, where they had discovered a well-defended cave complex, about 40 miles southwest of the Kurdish region’s capital city of Erbil.

About two-dozen ISIS fighters were killed and nine caves were destroyed, the Iraqi Counter-Terrorism Service said on Twitter on Monday, sharing photos of Iraqi troops on the rocky slopes.

Inherent Resolve officials did not respond to Stars and Stripes inquiries on the matter, but two unnamed military officials told the New York Times the Raiders were part of an assault that appeared to match that description.

Their deaths are the first combat fatalities in Iraq since last August, when a 35-year-old gunnery sergeant who was named the Corps’ top commando in 2018, Gunnery Sgt. Scott A. Koppenhafer, was killed during operations against ISIS in the expansive Nineveh province, also in the country’s north.

After once controlling a vast swath of Iraq and Syria, ISIS was routed from the last of that territory in Iraq in December 2018 and Syria last spring, but the group has continued to wage an insurgency and has used rugged mountain terrain and vast deserts to regroup and train, officials have said.

U.S.-backed Iraqi security forces have sought to eliminate ISIS militants who have taken refuge in some of the country’s rugged mountain ranges, including the Hamrin and Makhmour mountains west of Kirkuk, where the militants are reported to be training and regrouping.

More than 5,000 U.S. troops are deployed to both countries to help equip, train and support local partner forces battling the terrorist group, though some lawmakers in Baghdad called for the American troops to leave earlier this year, as a series of back-and-forth escalations between the U.S. and Iran played out on Iraqi soil. The U.S. briefly paused its support to Iraq’s anti-ISIS operations to focus on security in January.

The latest deaths have prompted a U.S. review of its support to those operations, unnamed officials told the New York Times on Monday.

The two American deaths this week are the first in the country in 2020 and bring to three the number of Americans who have died while deployed as part of the U.S. anti-ISIS coalition in Iraq and Syria this year. Spc. Antonio I. Moore, 22, of Wilmington, N.C., died Jan. 24 during a vehicle rollover accident while conducting route clearance operations in Syria’s Deir al-Zour province.

The effort to recover the dead this week, which took about six hours, required additional coalition troops, who “trekked through mountainous terrain and eliminated four hostile ISIS fighters who were barricaded in the caves,” Col. Myles B. Caggins III told the Times in a statement. The operation involved elite Delta Force operators and required hoisting the Marines out of a crevasse, the newspaper reported, citing unnamed officials.