A senior Pentagon official said there had been an indication that an Iraqi plane had gone down but that appeared not to be the case.

It was the first time that Iraqi fighters have clashed with US fighters since December 1992 when a US Air Force F-16 Falcon shot down an Iraqi MiG-25 after being illuminated by radar.

The BBC's Caroline Wyatt in Baghdad: No reaction from Iraq

The encounter, involving land-based air force F-15 and F-14s from the aircraft carrier USS Carl Vinson, occurred at 1015 Gulf time (0715 GMT), the official said. All returned safely to their bases.

A US military official, Major Joe LaMarca, said warplanes patrolling the zone responded after being "engaged" by Iraqi jets.

Speaking from Central Command headquarters in Tampa, Florida, he said no allied aircraft were lost. All returned safely to the aircraft carrier USS Carl Vinson.

He described it as the "most aggressive" incident involving Iraqi jets breaching the no-fly zone.

Latest incident

US and British planes patrol the zone, set up after the 1991 Gulf War.

US planes fired on ground missile batteries in that zone and in a northern no-fly zone last week after they said missiles had been fired at them from the ground.

This was the third incident in less than a week involving US warplanes enforcing the no-fly zone.

Speaking on Tuesday, Iraqi air force chief General Khaldoun Khattab Omar said: "Iraqi fighter planes are totally free to fly the skies of Iraq, in the north and the south.

"They have the right to defend our territory and no-one can stop them."