They said four air-to-air missiles were fired after about a dozen retreating Iraqi MIG and Mirage warplanes, which had violated the no-fly zone policed by American and British aircraft. One Iraqi jet apparently crashed while fleeing, but it did not appear to be hit by a missile. ``Missiles were fired at several Iraqi aircraft. One of them apparently went down, but there is no evidence that it was hit,'' one official at the Pentagon said, asking not to be identified. All US jets returned safely to their bases, according to a spokesman for the US Central Command in Tampa, Florida,which oversees American military operations in the Gulf.

The Pentagon said the incident occurred at about 2045 IST Major Joe Lamarca, a Central Command spokesman in Tampa, said military experts were still sorting through reports from the region and could not give further details. He said no allied aircraft were lost. Meanwhile, Iraq has requested that the United Nations replace its US and British humanitarian personnel in the country because it can no longer protect them from the ``deep popular anger'' after four days of US-British missile strikes.

In a note to the United Nations yesterday, Iraq clarified in writing what Iraqi officials told their UN counterparts in Baghdad last week, marking another dispute in the already fragile UN relationship with Iraq. ``The sense of anger that besets 22 million Iraqis may find expression in unfriendliness on the part of some of them vis-a-vis programme personnel of the United States or British nationality, particularly in the case where those dear to them werekilled in the barbarous United States and British bombardment,'' the note warned.

John Mills, spokesman for the UN programme in Iraq, yesterday said that Baghdad would allow four Britons and three Americans to remain in Iraq but would not renew visas for nine Britons and an American working with the humanitarian programmes.