BAGHDAD, Iraq (CNN) - U.S. planes on Sunday dropped eight bombs and fired three missiles on Iraqi military installations in response to anti-aircraft fire in the northern no-fly zone, a U.S. military official said.

The attacks occurred Sunday afternoon near the town of Mosul, about 400 kilometers (250 miles) north of Baghdad, said U.S. Air Force Capt. Mike Blass, spokesman for the U.S. European Command in Stuttgart, Germany.

Blass said the planes had struck an air defense headquarters, a radio relay site, and a surface-to-air missile site.

He described the mission as "ongoing."

The United States and Britain set up no-fly zones in the north and south of Iraq at the close of the 1991 Persian Gulf War to protect rebels operating in those areas. Iraq does not recognize the no-fly zones, and has vowed to shoot down "enemy" planes violating its airspace.