ANKARA, Turkey (AP) _ U.S. jets bombed air defense systems in northern Iraq for a third consecutive day Wednesday, after coming under Iraqi artillery fire, the U.S. military said.

U.S. warplanes were fired upon from sites near Bashiqah, 250 miles north of Baghdad, the Germany-based U.S. European Command said.

The aircraft bombed parts of an air defense system before safely returning to Incirlik air base in southern Turkey.

The United States has been enforcing northern and southern no-fly zones in Iraq since the end of the Persian Gulf War in 1991.

Iraq considers the zones violations of its territorial sovereignty and has been challenging the patrols since December 1998.