US President George W Bush has given the Iraqi leader Saddam Hussein 48 hours to leave or face war following what he called the failure of peaceful efforts to disarm the country.
Mr Bush urged Iraqi soldiers to surrender
A refusal by the Iraqi leader and his two sons to go would "result in military conflict, commenced at a time of our choosing," Mr Bush said in an address to the nation at 0100GMT on Tuesday.
His televised speech came just hours after the collapse of diplomacy at the UN Security Council.
More than 250,000 US troops are now stationed in the Gulf awaiting orders, along with UK and Australian troops.
But even before Mr Bush delivered his ultimatum, Iraqi Foreign Minister Naji Sabri said that "any child" in Iraq knew a demand for Saddam Hussein to go into exile would fail.
Reactions by world leaders to the ultimatum have so far been generally negative, with France accusing the US president of taking a "unilateral decision" that was "contrary to the will of the UN Security Council".
China committed itself to continuing efforts for peace "so long as there's one glimmer of hope", but Japan's Prime Minister Junichiro Koizumi voiced support for Mr Bush.
In other developments:
- Australia commits troops to any US-led attack
- UN weapons inspectors leave Iraq
- Turkish president ups pressure for vote on allowing US troops to deploy on Turkish soil.
- Lower chamber of UK parliament to debate war on Iraq
- Opponents of war led by France call for a UN Security Council meeting on Wednesday
In his address from the White House, Mr Bush said the US had the legal right to protect itself.
He warned that Iraq's weapons could be used against Americans by terrorists, including members of Osama Bin Laden's al-Qaeda network.
"The danger is clear," he said. "Using chemical, biological or, one day, nuclear weapons obtained with the help of Iraq, the terrorists could fulfil their stated ambitions and kill thousands or hundreds of thousands of innocent people in our country or any other.
"Instead of drifting along toward tragedy, we will set a course toward safety."
Minutes after Mr Bush finished his speech, US officials announced they had raised the terrorism alert to orange, the second-highest level.
Authorities warned of "multiple attacks" nationally and abroad in the event of a US-led war with Iraq.
Mr Bush advised all foreign nationals, including journalists and UN weapons inspectors, to leave Iraq immediately.
He stressed he believed in the mission of the UN and that the US and other countries had tried to ensure the peaceful disarmament of Iraq since the end of the 1991 Gulf war.
On Monday, diplomacy collapsed at the UN when the US, UK and Spain withdrew a draft resolution authorising the use of force against Iraq, amid threats of a veto from France.
Referring to France and Russia, Mr Bush criticised permanent, veto-wielding members of the UN Security Council who said they would not allow resolutions compelling Iraq to disarm.
"These governments share our assessment of the danger, but not our resolve to meet it," Mr Bush said, adding that many other countries supported US policy.
However it was seen as unlikely that the US and its allies could have raised the nine votes needed, even without a veto, to pass the resolution in the Security Council.
Mr Bush also used his 13-minute address to send a message to Iraqis, stressing that any military action would be directed against the "lawless men" in power - such as Saddam Hussein and his sons, Qusay and Uday.
"As our coalition takes away their power, we will deliver the food and medicine you need," the president said.
"We will tear down the apparatus of terror and we will help you to build a new Iraq that is prosperous and free."
He promised: "The tyrant will soon be gone - the day of your liberation is near".
The US leader urged Iraqi forces not to destroy oil wells or use chemical weapons.