American and Iraqi warplanes have clashed over the American-imposed air exclusion zone in southern Iraq.

It's the first time since the American and British raids on Iraq last month that an air-to-air engagement has been reported.

American military officials say that a number of Iraqi jets entered the zone and were challenged by four patrolling aircraft, which fired missiles.

They could not say if any of the missiles hit, and Baghdad denied any of its planes were missing.

Iraq does not recognise the exclusion zones and in the past week its ground forces have twice opened fire on aircraft patrolling them.

On both occasions, the aircraft retaliated by attacking the Iraqi missile batteries involved.