WASHINGTON (Reuters) - U.S. warplanes struck an air defense site in Iraq on Monday after aircraft on patrol in the southern no-fly zone encountered hostile Iraqi fire, the U.S. military's Central Command said.

All U.S. aircraft returned safely from the area. There was no immediate report of damage on the ground.

U.S. and British jets have been policing no-fly zones in northern and southern Iraq for more than a decade. The zones were set up after the 1991 Gulf War to protect Kurds and Shiite Muslims from attack by Iraqi President Saddam Hussein's military.

The last coalition strike in the southern no-fly zone was against an Iraqi anti-aircraft artillery site on Jan. 21, the military said in a statement.