F-16 Fighting Falcon

WASHINGTON (CNN) -- A U.S. Air Force F-16 fighter flying over Iraq's southern no-fly zone fired a radar-seeking missile at an Iraqi radar site Tuesday morning, Pentagon officials said.

Pentagon officials said the HARM missile was fired near Basra, after four British Tornado jets on routine patrol said they believed they had been "locked on" by Iraqi radar -- a move that could mean that an Iraqi missile could be fired at them at any time.

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Initial reports did not make clear whether the lock-on process -- which U.S. military officials have described as a potentially very hostile act -- was done deliberately or by accident.

Pentagon officials described the missile firing as a defensive measure. The incident occurred around 9:30 a.m. Iraqi time (1:30 a.m. EDT).

Early reports also did not make it clear whether the Iraqi radar position was hit or not.

None of the planes were harmed or fired upon, Pentagon sources said.

The incident comes at a time of lessening tensions between Iraq, allied forces, and U.N. weapons inspectors.

The southern no-fly zone was created in 1991 after the Gulf War to prevent the Iraqi government from attacking Shiite Muslims in the area. There is a similar no-fly zone in northern Iraq to protect the country's Kurdish minority.