The U.S. has claimed Iraq has already breached the terms of the UN resolution, just 24 hours after the first weapons inspectors arrived in Baghdad.

Iraq anti-aircraft gunners fired at American and British jets patrolling the northern no-fly zone Monday, the U.S. said.

This is not unusual. The Iraqis have been firing on jets in the no-fly zones since they were established; allied pilots fire back with missiles.

The UN has not sanctioned the no-fly zones, which were unilaterally imposed by the U.S. and Britain after the Gulf War.

But even though the exchanges between pilots and anti-aircraft gunners have been going on for years, the U.S. said Monday's attacks were especially significant.

"The United States believes firing on our aircraft in the no fly zone or the British aircraft is a violation is a material breach," said White House Press Secretary Scott MacClellan, referring to UN Resolution 1441.

He said the resolution forbids Iraq from attacking countries enforcing it.

U.S. Secretary of Defense Donald Rumsfeld says there are legitimate grounds to complain to the UN Security Council, but it may be too early to act now.

"It is for the President of the United States and the UN Security Council to make judgments of their view of Iraq's behaviour over a period of time, and those negotiations and discussions are just starting," said Rumsfeld.