Iraqi radio said missiles had hit President Saddam Hussein’s family home in the capital during an initial attack at dawn.
President George Bush appeared on television at 0315 GMT (8.15am PST) to announce that US-led forces had formally launched a strike against Iraq, promising a “broad and concerted campaign” to disarm Baghdad and topple President Saddam Hussein.
As buildings blazed in Baghdad, officials in London and Washington said units of the US Marine 1st Expeditionary Force and British Royal Marines had crossed into southern Iraq after nightfall.
But US officials said the troop movement and the fresh wave of night bombing did not represent a massive military attack predicted by Defence Secretary Donald Rumsfeld earlier in the day.
“The whole thing is kicking off tonight,” a British military source said on condition of anonymity. “British forces are engaged.”
US officials cautioned the big blitz was still to come.
“This is all part of the preparation” for a major ground attack, one said. “There will be things that you see and things that you don’t.”
Targets in Baghdad included buildings around the planning ministry in the centre of the city and in the southeast. The office of Deputy Prime Minister Tareq Aziz had been hit.
Iraqi radio said there were no casualties in the attack on Saddam’s family home.
About 280,000 US and British troops are in the Gulf region, many of them in Kuwait.
US and British forces crossed the Iraq-Kuwait border after intense artillery barrages.
Kuwait’s KUNA news agency said they had seized the Iraqi border town of Umm Qasr, a port.
A correspondent travelling with US Marines said an unspecified number of Iraqi troops had surrendered.
An Iraqi military spokesman said a US troop-carrying helicopter had been shot down.
Earlier explosions reported along the frontier and in the direction of the southern Iraqi city of Basra.
“The first lot of big explosions came from the direction of Basra and then there were more west of that direction,” reports from near the border said.
“There are a lot of flashes on the horizon, we can hear the thuds in the distance,” a correspondent said.
At last one US unit reported coming under Iraqi fire.
“A US unit was targeted by Iraqi mortar fire this evening on the Kuwait-Iraq border,” a US military source said. There was no information on casualties.
Officials in Baghdad said four Iraqi soldiers died in attacks on Thursday and that Washington had fired 72 cruise missiles.—Agencies
Our correspondent adds from Washington: The United States modified its schedule for an invasion of Iraq late on Wednesday night after the CIA received information that senior Iraqi leaders, including President Saddam Hussein, were gathering at a residence in southern Baghdad.
The CIA argued to US leaders that if the attack were delayed, Iraqi leaders might disperse. It was not clear if any Iraqi leader was killed in the attack.
Early reports from the BBC said British troops that are part of coalition forces were not told in advance about the attack, dubbed “decapitation strike”.
The attack began 90 minutes after the deadline for President Saddam to go into exile ended at 6am PST.
US officials in Washington told reporters that the military targeted a residence in Baghdad after the “senior Iraqi leadership” arrived there. The information came “in a fairly timely fashion” some time on Wednesday afternoon, compelling a fast strike before the Iraqi leaders left.
Officials at the White House described the attack as “a decapitation attempt”.
They did not identify the leaders but the strikes encouraged rumours in Washington that Iraqi President Saddam Hussein was also one of the targets. A defiant Saddam, however, appeared on national television shortly after the attack to quash these rumours.
The CNN said more than 40 cruise missiles and several F-117 Nighthawk fighter jets were unleashed against at least two time-critical targets — one in Baghdad and one south of the city.
The NBC said B-1, B-2, and B-52 bombers also took part in the strike against a “key air node” and a “national command centre.” A senior official may also have been targeted, according to NBC and CNN.