WASHINGTON >> Two U.S. Special Operations personnel were killed in northern Iraq on Sunday during an operation against Islamic State fighters, military officials said today, marking the first combat deaths of 2020 in the nearly six-year U.S. campaign against the terrorist group.

The Americans killed were part of a Marine Special Operations team, according to two military officials, and were clearing a large, well-defended cave complex alongside Iraqi counterterrorism forces in mountains near Makhmur, roughly 40 miles south of Irbil.

In a statement, Col. Myles B. Caggins III, a spokesman for the U.S.-led mission in Iraq and Syria, said U.S. troops had to deploy additional forces to recover the dead in an effort that took about six hours.

“The forces trekked through mountainous terrain and eliminated four hostile ISIS fighters who were barricaded in the caves,” Caggins said, using an acronym for the Islamic State.

According to one military official, the Americans who were killed had to be pulled out with a hoist after falling into a crevice, and it is unclear how many Iraqi forces were killed and wounded.

Initially, the U.S.-led mission in Iraq and Syria gave scant details about the episode in a news release today, pending the notification of the families of those killed.

The deaths come as the Islamic State has spent recent months reconstituting its ranks in porous and ungoverned areas in Iraq and Syria, leaving local forces in both countries working to keep the terrorist group away from urban areas.

In a tweet, Brett McGurk, the U.S. special envoy for the coalition to defeat the Islamic State until 2018, pointed to the length of time it took to recover the dead. “Something is not right,” he said.

“We seem to have lost focus on this mission while increasing risks to our people and depleting their resources for no good reason,” he wrote.

In January, after a U.S. airstrike in Baghdad killed a top Iranian military officer, Gen. Qassem Soleimani, the U.S.-led mission in Iraq suspended its mission against the Islamic State in the country for 10 days, hunkering down in fear of Iranian retaliatory strikes.

After the Iraqi government accused the United States of violating the country’s sovereignty with the strike, parliament called for the expulsion of all U.S. forces from the country, roughly 5,200 troops.

The last American killed in combat in Iraq was in August, when Marine Gunnery Sgt. Scott A. Koppenhafer died during a joint Iraqi-U.S. operation in Nineveh province against the Islamic State. The Pentagon is currently weighing options to draw down forces in Iraq to around 2,500.

At its height, the Islamic State’s self-declared caliphate was the size of Britain and controlled the lives of up to 12 million people.