On what UN chief Kofi Annan said was a “sad day” for the world, Baghdad was virtually a ghost town as residents fled but there was little sign of Iraqi military preparations for a conflict likely to change the face of the Middle East. After Bush formally told Congress war was now the only recourse, White House spokesman Ari Fleischer said the administration hoped for a short conflict but warned of “many unknowns”.

“Clearly, one of the major concerns we have is that we are up against an enemy who may use chemical or biological weapons,” he said. “Americans have to be prepared for loss of life.”

Hours before the deadline, King Hamad of Bahrain offered asylum to Saddam.

But Iraqi Deputy Prime Minister Tareq Aziz — appearing in public to deny rumors he had defected — said it was “impossible” Saddam would flee.

Saudi Arabia also denied that it had proposed that Saddam Hussein go into exile. The state-run Saudi Press Agency quoted what it called an official source as dismissing the report as “baseless”.

Caught in a swirling sandstorm in the northern Kuwait desert, US and British troops advanced to the border where a UN-patrolled demilitarized zone was set up after the 1991 Gulf War.

“All elements of the US armed forces are currently repositioning close to the Iraq border,” said one US commander, Colonel Will Grimsley.

Iraqi officials told Bush he was sending his troops to certain death as legislators meeting at an emergency session pledged to shed their blood to defend the man who has led them since 1979.

“History will recall how the people of Iraq, under the glorious leadership of Saddam Hussein, inflicted a lesson on the worthless,” the assembly said in a unanimous declaration rejecting the US ultimatum.

Aziz, one of the most familiar faces in Saddam’s regime, said the rumors he had defected were “sapping the morale” of the Iraqi people.

In Kuwait however, a US officer said 15 Iraqi soldiers had crossed the border and surrendered, while an official with one of the Kurdish factions that controls northern Iraq said a number of Iraqis “with minor responsibilities” had defected to Kurdish areas.

At the United Nations, Annan said it was a “sad day” for the world and reminded the United States and Britain of their legal duty to protect Iraqi civilians.

“I know that millions of people around the world share this sense of disappointment and are deeply alarmed by the prospect of imminent war.” Yesterday, the Security Council turned its attention to fears of a humanitarian catastrophe with officials working on plans to cope with a possible flight of 600,000 Iraqi refugees.

Already, tens of thousands of people have been pouring into northern Iraq’s autonomous Kurdish region from government-controlled areas and neighboring Turkey and Jordan are bracing for waves of refugees.

“Our task now is to do everything we possibly can to avert a humanitarian disaster,” German Foreign Minister Joschka Fischer said at the meeting, which was boycotted by his British and US counterparts.

In Turkey, the government said it will ask Parliament today to approve overflight rights for US aircraft but has lost a six-billion-dollar aid package after failing to allow US troops on its soil.

British Prime Minister Tony Blair told Parliament that ousting the regime was the chief goal and said senior officials “will be held accountable for what they have done,” implicitly suggesting Saddam himself could be tried for war crimes.

In a ghostlike Baghdad, residents were scrambling to gather stocks of food, medicines and fuel but most shops had shut their doors and prices for basic supplies had doubled or tripled and the value of the dinar tumbled.

“We are not wondering whether there would be war anymore,” said one taxi driver. “We are just anxious about the exact time the bombs will start raining on Baghdad, our great Arab ancient city before the eyes of a heedless world.”