BBC's Philippa Thomas: US may be preparing for further military action

Speaking to reporters on Tuesday after a clash between US and Iraqi jets, Pentagon spokesman Ken Bacon said: "We have shown our willingness to strike with surprising force in the past, and that remains an option in the future."

The chairman of the US Joint Chiefs of Staff similarly told Congress that more strikes were possible.

Shelton warns of possible action

When asked by the Senate Armed Services Committee why American missiles and jets were not being used to destroy Iraqi military airfields and jets on the ground, General Henry Shelton said:

"We have looked at numerous options and have various plans that are available right now. If the president were to see fit to take that type of action, we in fact have these kinds of plans on the shelf."

Speaking later on television, Secretary of State Madeleine Albright was also emphatic that the US would enforce the no-fly areas.

Missiles fired over Iraq

Tuesday's incidents came over southern Iraq.

Officials in Washington said four US aircraft fired six air-to-air missiles at four Iraqi planes although none hit their targets.

One Iraqi fighter was reported to have crashed, possibly after running out of fuel. All US aircraft returned safely to base.

Mr Bacon said there had been a total of eight violations of the southern no-fly zone, involving as many as 14 Iraqi jets.

The Iraqi military denied it had lost a plane in the incident. A spokesman told the official Iraqi news agency that Iraqi jets had "confronted" allied aircraft that had "violated" Iraq's air space. The spokesman said all planes returned safely.

It was the first clash between Iraqi and US fighters since December 1992, when a US Air Force F-16 Falcon shot down an Iraqi MiG-25 after being illuminated by radar.

Latest incident

Two no-fly zones - one in the north and one in the south of Iraq - were set up after the 1991 Gulf War. They are patrolled by US and UK planes.

Saddam Hussein: "People of the Arab World, rise against the foreigners"

Last week, US planes fired on ground missile batteries in both zones after they said missiles had been fired at them from the ground.

The latest incident was the third in less than a week involving US warplanes enforcing the no-fly zone. BBC Washington Correspondent Philippa Thomas said it was the most serious since the US and UK bombed Iraq in December in Operation Desert Fox.

Following the clash, a speech was broadcast by Iraqi President Saddam Hussein calling for Arabs to overthrow any of their leaders supporting the US.

Damage assessment

In another development, a preliminary assessment of damage to civilian facilities caused by the US-led strikes on Iraq - by the UN children's fund Unicef - said a food warehouse, schools, medical and maternity centres and a water supply system had been hit.