The Pentagon on Friday identified the Army Ranger killed in Afghanistan the day prior.

Sgt. 1st Class Christopher Andrew Celiz, 32, of Summerville, S.C., was killed Thursday by enemy small arms fire “while conducting operations in support of a medical evacuation landing zone,” according to a Pentagon press release.

Celiz was assigned to the 1st Battalion, 75th Ranger Regiment, Hunter Army Airfield, Ga., according to the release.

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The incident happened in Zurmat district, Paktia province, in eastern Afghanistan, the release said.

The release does not specify which of Afghanistan’s insurgent or terrorist groups were involved, but the area is home to Taliban militants. Additionally, Army Rangers in the past have conducted raids on al Qaeda training camps in the area.

In addition to Celiz, an Afghan security force member was killed and several were wounded in the incident, the U.S. military said Thursday.

“The incident is under investigation,” Friday’s release said.

Celiz is the fourth U.S. service member killed in combat in Afghanistan this year and the second in less than a week.

On Saturday, Cpl. Joseph Maciel, 20, was killed and two others were injured during an apparent insider attack at a small base in Tarin Kowt, Uruzgan province. That incident is also under investigation.

The United States has about 16,000 troops in Afghanistan on a dual mission of training, advising and assisting Afghan forces in their fight against the Taliban and conducting counterterrorism missions against groups such as al Qaeda and the Islamic State in Iraq and Syria.