UNITED NATIONS, Nov 4: Iraq has threatened to shoot down United States surveillance planes (U-2 spy planes) that fly over its airspace as part of United Nations weapons inspections team, US Ambassador Bill Richardson said today.

Iraqi Ambassador Nizar Hamdoon sent a letter last weekend to Chief Weapons Inspector Richard Butler warning him that Iraqi forces were on alert for a possible US air strike.

The letter warned Butler that he must assume responsibility for authorising surveillance flights especially in the circumstances in which ``our anti-aircraft artillery is open everywhere in anticipation of possible aggression.'' it said.

However, Butler said the inspections will go on and the U-2 plane will continue to fly

Richardson called the Iraqi threat an ``irresponsible escalation'' of the crisis between the United Nations and Iraq and a threat to escalate the confrontation into a military showdown.

``This is a direct threat on the United Nations,'' Richardson told reporters following a meeting at UN headquarters.

Sunday night's letter from Hamdoon was the first sign of an unequivocal threat to use force against the United Nations.

Iraq maintains that it is not acting against the UN but against the United States, which it accuses of using the inspections for its own spying.

Earlier, the UN inspectors withdrew for the second consecutive day from three sites after Iraqi officials told the chemical, biological and long-range missile sector teams that they could continue their work only without their American colleagues, UN spokesman Ewen Buchanan said.

``In accordance with their instructions, the chief inspectors withdrew,'' he said, adding Butler has asked inspectors to withdraw than accept Iraqi terms.Meanwhile, three envoys, dispatched by UN Secretary General Kofi Annan with the mandate to `convince Iraq to cooperate and not to negotiate', would reach Baghdad tomorrow and return to New York over the weekend to report to the Security Council on Monday.

Annan was hopeful the team, comprising an Algerian, an Argentinian and a Swede, would be able to meet Iraqi President Saddam Hussein, who the Secretary General hoped would not implement the Wednesday deadline to expel the Americans inspectors `while he was talking to the team'.

Copyright © 1997 Indian Express Newspapers (Bombay) Ltd.