UK Prime Minister Tony Blair has won key support for a military campaign against Saddam Hussein, despite a major rebellion in his Labour Party.
Mr Blair suffered the greatest parliamentary revolt of his premiership when 139 of his party colleagues voted for an amendment saying the case for war was not yet proven.
But the government still managed to beat the rebel amendment and see its own motion supporting the use of UK forces in Iraq passed by a large majority - 412 to 149.
The vote came after the United States said its troops would invade Iraq even if President Saddam Hussein complied with an ultimatum to quit his country.
US President George W Bush said there would be military action if Saddam Hussein and his sons did not leave Iraq by 0100 GMT on Thursday - a demand rejected out of hand by the Iraqi leadership.
Turkey, meanwhile, could yet give US forces the option to attack from the north. The government announced it will ask parliament to vote again on allowing US troops to use its land and air bases, but it is not clear when the vote will be held.
Mr Bush's spokesman Ari Fleischer said soldiers would need to go into Iraq to search for weapons of mass destruction.
He warned the Iraqi leader that he would be making a "final mistake" if he did not leave by the deadline set by Mr Bush.
Hours after Mr Bush's broadcast, Saddam Hussein appeared on television himself, dressed in a military uniform, as the US ultimatum was rejected.
A statement from a cabinet meeting chaired by the Iraqi president said Iraq and all its people were "fully ready to confront the invading aggressors and repel them".
Saddam Hussein's defiance was echoed by Iraqi Foreign Minister Naji Sabri who denounced Mr Bush's as "a war criminal" and accused Washington of trying to "push the United Nations to suicide".
Washington "wanted to use the UN like an office to issue a permit to go to war," Mr Sabri said.
He also criticised the UN's decision to withdraw it staff from Iraq, saying it ran contrary to the world body's responsibilities and had "paved the way for American aggression".
Reporting from the Iraqi capital Baghdad, the BBC's Paul Wood says Iraqis are making final preparations for war - mainly buying food and fuel.
In other developments:
Mr Bush's 48-hour ultimatum - delivered in a televised speech at 0100 GMT on Tuesday - received widespread international criticism.
- Hans Blix - the head of the UN arms inspectors now recalled from Iraq - said he doubted that Baghdad would use chemical or biological weapons in a war even if it possessed them; he will give a further report to the Security Council on Wednesday
- An emergency session of the Iraqi national assembly has been called for Wednesday morning
- US Secretary of State Colin Powell said 45 nations had joined Mr Bush's "coalition of the willing" - 30 were happy to make their support public while 15 preferred to remain unnamed at the moment
- Spanish Prime Minister Jose Maria Aznar - a strong supporter of President Bush's Iraq policy - was barracked during a stormy session of parliament when he announced that Spain would not send combat troops to the Gulf
- More foreign diplomats have left Baghdad
Countries seeking a peaceful outcome to the crisis condemning Washington's decision to abandon diplomacy and questioning the legality of starting a war.
In his strongest statement yet on the Iraq crisis, Pope John Paul II warned the leaders of the forces gathered against Iraq that they face a grave responsibility before God if they go to war.
However, in an apparent softening of its position, France, one of the staunchest opponents of conflict, said that if Iraq uses weapons of mass destruction it may consider assisting the war effort.
"If Saddam Hussein were to use chemical and biological weapons, this would change the situation completely and immediately for the French Government," France's Ambassador to the US, Jean-David Levitte, said.