United States warplanes have fired a missile at an Iraqi anti-aircraft position in northern Iraq.

An Iraqi statement said four soldiers were killed and seven were wounded before Iraqi air defences forced the enemy aircraft to turn back.

The Americans say they retaliated after Iraqi missiles were fired at them.

President Clinton said the response was appropriate, and American forces would continue to enforce no-fly zones over northern and southern Iraq.

Iraq disputes the legality of the air exclusion zones, and previously warned that it would fire on Western aircraft violating its air space.

It's the most serious confrontation since the recent British and American air strikes against Iraq.