WASHINGTON, March 18: President George Bush has given President Saddam Hussein and his sons 48 hours to leave Iraq, warning that if they fail to do so by Thursday morning US forces will invade Iraq.

The military action would “commence at a time of our choosing,” Mr Bush told an international television audience on Monday evening.

But officials in Washington said massive airstrikes on Iraqi targets might begin late on Thursday or early Friday.

The United States already has more than 250,000 troops in the region, ringing Iraq along with thousands of British and Australian soldiers.

Mr Bush’s speech came hours after the United States, Britain and Spain announced they would not put their draft UN resolution on Iraqi disarmament to a vote in the Security Council.

Going beyond his earlier demand for Iraq to disarm, Mr Bush sought unconditional removal and exile of “the Iraqi dictator and his cohorts”. “It is too late for Saddam Hussein to remain in power,” he said.

Mr Bush told the American people that if President Saddam Hussein chose confrontation, “every measure will be taken to win the war as every measure has been taken to avoid it.”

“Americans understand the costs of conflict because we have paid them in the past. War has no certainty except the certainty of sacrifice.”

But if battle became necessary, Mr Bush said, “the only way to reduce the harm and duration of war is to apply the full force and might of our military, and we are prepared to do so.”

He called on Iraqi soldiers to “act with honour and protect your country by permitting the peaceful entry of coalition forces to eliminate weapons of mass destruction.”

Urging the Iraqi forces “not to fight for a dying regime that is not worth your life,” he asked them to surrender to the US troops. “Clear instructions will be given on actions you can take to avoid being attacked,” he told the Iraqi soldiers.

The US president also warned the Iraqi forces not to destroy the country’s oil fields, which he said belong to the Iraqi people, or use any of the chemical, biological or nuclear weapons that Iraq allegedly possesses. “War crimes will be prosecuted. War criminals will be punished. And it will be no defence to say ‘I was just following orders’.”

Mr Bush also urged journalists, arms inspectors and humanitarian workers to leave Iraq as soon as possible.

Earlier in the day, UN Secretary-General Kofi Annan ordered UN workers to leave. Mr Bush’s deadline will be 48 hours after he completed his remarks, about 4:15am Thursday Iraqi time.

Mr Bush’s father followed a similar path in 1991, giving Iraq until Jan 15 to abandon Kuwait with coalition forces beginning hostilities early Jan 16. The senior Bush spoke to the American people as cruise missiles began landing in Baghdad.

Warning that an attack on Iraq could raise dangers elsewhere, Mr Bush announced “Operation Liberty Shield,” a comprehensive, national plan that increases security at America’s borders and its transportation systems, and readies federal response resources in the event of a terrorist attack. Within minutes of his mentioning the effort, the Department of Homeland Security raised the threat level to “high” and began tightening up border locations. Very quickly, both Democrats and Republicans fell in behind Mr Bush. “Like many Americans, I have raised questions about whether military action at this time is the best way to disarm Saddam Hussein, and whether we have exhausted every other alternative. Sadly, we stand on the brink of war,” said Rep. Nancy Pelosi of California, House Democratic leader. “If our troops are ordered into action, Americans will support and stand united behind our courageous men and women in uniform who will bear the burden of that action.” Senate Democratic leader Tom Daschle said: “If the president decides that force is the only remaining option to disarm Saddam Hussein, Democrats and Republicans will be unanimous in our strong support for our troops and for ensuring that they have all the tools and resources needed to be successful.”

Sen. Joseph Biden, D-Del., said it was important to support the president and that leaders were assured during discussions that Mr Bush would deliver a second speech to the American people to talk about his vision for what happens after the war is over.

“I have been assured — though I am not satisfied — that there is a clear plan for after the shooting stops,” Mr Biden said.