Story highlights The strike took place Saturday, 120 miles north of Mogadishu at a training site

A U.S. official told CNN that the Al-Shabaab fighters were standing outside in military formation when the strike occurred

Washington (CNN) In a move to stop what the U.S. military said was an imminent threat against U.S. troops and African peacekeeping forces in Somalia, a U.S. strike in Somalia killed as many as 150 suspected Al-Shabaab fighters, the Pentagon said Monday.

The Pentagon initially characterized the attack as a drone strike, but later clarified that the operation involved both manned and unmanned aircraft.

The strike took place Saturday, 120 miles north of Mogadishu at a training site called "Raso Camp," according to Pentagon spokesman Capt. Jeff Davis.

The camp had been under observation by U.S. Special Operations forces for several weeks, Davis said. The camp had about 200 fighters on site including Al-Shabaab trainers.

Separately, a U.S. official told CNN that the Al-Shabaab fighters were standing outside in military formation when the strike occurred.

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