The two American F-14 tomcats and two F/A-18 hornets returned safely to the USS Carl Vinson in the Gulf, according to the US central command outside Tampa, Florida, and the Pentagon.

``The Americans responded to a threat initiated by two Iraqi MIG-21s flying south of 33rd parallel in Iraq and ground fire from anti-aircraft artillery,'' said Lt Col Mike Milord, a Pentagon spokesman.

The American planes dropped laser-guided bombs on two Iraqi surface-to-air missile systems. A damage assessment of the sites was still under way, a US official said today. US National Security Council spokesman David Leavy said today's incident would not alter US resolve to enforce the flight-interdiction zones that Saddam agreed to at the end of the 1991 Gulf war.