Washington (CNN) -- The Afghanistan battle that resulted in a rare fatality for a classified Army unit pitted U.S. troops against waves of insurgents who attacked from bunkers and caves, a U.S. military official said Wednesday.
American forces had to be reinforced several times during the two-day firefight in southeast Afghanistan's Paktika province, said the official, who declined to be named because he was discussing the Army's Special Operations Command. The sole U.S. fatality in the attack was Army Master Sgt. Benjamin A. Stevenson, a highly decorated member of one of the Army's special mission units.
The death in combat of a soldier from one of these highly trained units is rare, with the last occurring nearly a year ago, the official said. The classified units are sometimes publicly referred to as Delta Force, the Army equivalent of the Navy SEAL team that killed al Qaeda leader Osama bin Laden in May.
In the Paktika raid, U.S. and Afghan troops attacked an insurgent encampment under cover of darkness last week, killing nearly 80 foreign fighters -- mostly Arabs and Chechens brought into Afghanistan from Pakistan, the military official said.
But as they searched the site in the daylight, they were attacked by two more waves of insurgents who came out from underground bunkers and caves. Additional U.S. forces were called in several times as reinforcements as the firefight stretched on.
Stevenson, 36, from Canyon Lake, Texas, was on his 10th tour of duty in the war zones of Afghanistan and Iraq when he was killed Thursday. The military official said he died shortly after being evacuated from the battlefield, but the Pentagon has disclosed no other details.
The story behind his death offered a rare glimpse into the work of U.S. special operations units.
The target of last week's raid was a camp full of fighters from the so-called Haqqani network, which is responsible for many recent attacks in Afghanistan and is closely tied to al Qaeda. The presence of so many foreign fighters among an insurgent group that typically relies on local Afghan and Pakistani populations for manpower is a worrisome trend, according to a second U.S. military official.
"This is how they are expanding their capabilities," the official said.