The US on Thursday morning launched its attack on Iraq after its deadline for President Saddam Hussein and his sons to leave Iraq expired at 2000 EST [0630 IST, 0100 GMT].
"The opening stages of the disarmament of the Iraqi regime have begun," White House spokesman Ari Fleischer announced in Washington.
Later, in an address to the nation, US President George Bush made it clear that the aim was a regime change in Iraq.
Anti-aircraft fire was heard in Baghdad early in the morning. Significantly, there is no blackout in the city.
The US said it had begun the assault by firing a Cruise missile at a 'target of opportunity' in Iraq in what appeared to be a surgical strike on the Iraqi leadership. But it now appears that more have been fired since then.
US troops, however, have not yet crossed the Iraq-Kuwait border.
US President George Bush addressed the nation at around 2215 EST (0830 IST) and made it clear that the aim of the attack is to change the regime in Iraq, saying US forces had begun the campaign to free the people of Iraq from Saddam Hussein.
In the four-minute address, Bush reiterated his claim of Saddam possessing weapons of mass destruction and said the US would try to make the campaign as short as possible.
"On my orders," Bush said, "coalition forces have begun striking at selected targets."
These are the opening stages of what would be a broad and concerted campaign. More than 35 countries are giving crucial support from the use of naval and air bases to help with intelligence and logistics for the deployment of combat units, Bush said.
"In this conflict, America faces an enemy who has no regard for the conventions of war or rules of morality," he said.
"Saddam Hussein has placed Iraqi troops and equipment in civilian are as, attempting to use innocent men, women and children as shields for his own military, a final atrocity against his people." Bush claimed.
At this hour, American and coalition forces are at the early stages of military operations to disarm Iraq, to free its people and to defend the world from grave danger, Bush said.
He told Americans that US troops will try to cause minimum causalities among civilians and hoped that they would come back at the earliest safe and sound.
Baghdad Radio on Thursday morning made an announcement about the beginning of war saying 'May god protect us from the invaders'.