A U.S. F-16 fighter bombed an Iraqi surface-to-air missile system Tuesday after Iraq moved it deep into the southern no-fly zone, defense officials said.

The mobile SA-13 missile system was at a site called Qalat Sal, about 30 miles from the Tigris River city of Al Amarah, military officials said. The F-16 fighter dropped two bombs on it at about 6 a.m. EST, officials said.

Al Amarah, about 165 miles southeast of Bagdad, is inside the southern no-fly zone set up and patrolled by British and American planes since the Persian Gulf War to keep Iraqi forces from flying there.

Iraq says the patrols violate its sovereignty, and its forces frequently shoot at allied pilots both in the northern zone set up to protect the Kurdish minority and the southern zone to protect Shiites. Iraq has never shot down a coalition warplane patrolling either no-fly zone.

The Soviet-built SA-13 system — a missile battery mounted on a tank-like armored personnel carrier — had not fired on any coalition planes, military officials said. The United States says the mere presence of such air defense systems in the no-fly zones is a threat to pilots monitoring the areas.

The SA-13 missiles are effective only up to about 11,000 feet, however, and the planes patrolling the no-fly zone usually fly higher than that.

"Coalition strikes in the no-fly zones are executed as a self-defense measure in response to Iraqi hostile threats and acts against coalition forces and their aircraft," said a statement Tuesday from the U.S. Central Command, which monitors the southern zone.

The last previous strike in the south was Dec. 1, when planes targeted air defense facilities between Tallil and Al Basrah. In the north, two U.S. F-16s aimed four precision-guided weapons last Wednesday at elements of Iraq's air defense system near Mosul after Iraqis fired anti-aircraft artillery, said the U.S. European Command, which handles that zone.

Though the hostilities have become almost routine, they come as the Bush administration plans a possible war against Iraq to force it to give up weapons of mass destruction that officials say President Saddam Hussein could share with terrorists. Baghdad denies it has such weapons programs.

Defense Secretary Donald H. Rumsfeld has said the United States considers hostile actions in the no-fly zones to be violations of the latest U.N. Security Council resolution demanding that Iraq disarm. U.N. Secretary General Kofi Annan and some other Security Council members say they disagree with that view.