The Iraqi capital was virtually surrounded and US Army forces fanned out further in the city while Marines in thousands of armoured vehicles poured in from the east after clearing road jams at a key bridge crossing.

US tanks battled across Baghdad's main presidential compound -- a symbol of Saddam's iron-fisted rule -- amid heavy exchanges of tank, artillery and gun fire on day 20 of the war to oust President Saddam Hussein.

Mystery surrounded the fate of the Iraqi leader after US strikes Monday obliterated a building where he was believed to be meeting with his two sons.

Fresh waves of airstrikes pounded the southern and southeastern fringes of the city, while in the centre, two US tanks captured a key bridge over the river Tigris, where they met stiff resistance from Iraqi forces.

Baghdad took on the appearance of a ghost town later in the day, with even armed fighters off the streets in large parts of the city.

An eerie silence hung over the capital, plunged into darkness by a power cut, with sporadic explosions heard from the southern rim of the city.

US President George W. Bush, meeting chief ally British Prime Minister Tony Blair in Belfast, said he did not know if Saddam was dead or alive after Monday's targeted bombing.

"I don't know whether he survived ... The only thing I know is that he is losing power... Saddam Hussein will be gone," Bush said after his third meeting with Blair in as many weeks.

With focus shifting to a post-war Iraq, Bush pledged that the United Nations would have a "vital role" to play in rebuilding the shattered country, denying a reported split over the UN's role in supervising an interim Iraqi government.

Britain wants the UN to oversee any interim Iraqi military administration while Washington has sought initial US-British military control.

French President Jacques Chirac reiterated his insistence that the world body -- not the United States -- play the chief role in post-war reconstruction.

In London, Iraqi opposition groups said they would meet in the southern Iraqi city of Nasiriyah on Saturday to discuss the country's future.

Three journalists were meanwhile killed in US assaults in the Iraqi capital.

Ukrainian cameraman Taras Protsyuk from the Reuters news agency and Jose Couso, a cameraman from Spanish televison station Telecinco, were killed when a US tank fired on the Palestine Hotel, where foreign journalists have been staying.

The US military said the tank had fired a single round at the hotel after coming under grenade and small arms fire from the building. Journalists in the building denied that there was any gunfire from the building.

Three other Reuters staff members were also injured in the attack.

A correspondent for the Al-Jazeera Arabic television network was killed and a cameraman was injured after the station's offices were hit in a separate attack that the Qatar-based network said was a deliberate US strike.

The US military denied deliberately hitting Al-Jazeera.

Spain said it would ask the United States for an explanation of the Spanish cameraman's death, which brought to at least 12 the number of journalists and staff killed in the 20 days since war broke out.

One US Marine was also killed and six others wounded in firefights in the suburbs of Baghdad, hours after they had completed their final advance into the capital, US military officials said.

As the fighting raged in the city, Bush and Blair ended a two-day summit in Belfast, where the British leader said Saddam's regime was coming to an end.

"In all parts of the country our power is strengthening, the regime is weakening and Iraqi people are turning towards us," he said.

A US commander said that an A-10 Thunderbolt strike aircraft was shot down over Baghdad and crashed, but the pilot ejected and was rescued.

Thousands of armoured vehicles were pouring into the capital, with US military officials saying the end of Saddam's hold on power was near.

"We just continue to seize the initiative, will continue to push. Hopefully the regime will fall. It's just a matter of time," said Major Mike Birmingham, from the US infantry.

US forces continued to fan out across Baghdad, and were only a few kilometres from surrounding the city, officers said.

But Iraqi Information Minister Mohammad Said al-Sahhaf remained defiant, telling journalists US forces would surrender "or be burned in their tanks."

Hundreds of families fled the intensive bombing, driving eastwards in cars, trucks and minibuses overflowing with mattresses, kitchen utensils, beds and food, AFP correspondents reported.

"I'm closing the house and leaving with my family for a safer place. I will come back every now and then to see if something happened," said Ali Rishek, 53, before driving away with his wife and their three children.

The chief of staff of British forces in the Gulf warned of a potential "final act of defiance" by Saddam, with the collapse of his regime looking "inevitable."

"There is always the possibility that they were able to organise some final act of defiance -- and we've got to keep on our guard against that," said Major General Peter Wall.

The fate of Saddam continued to tease and taunt the United States. "We just don't know who might have been killed," one Washington official said after Monday's air assault in Baghdad.

"Obviously we hope that some part of the leadership was taken out of action, but we don't know at this point who might have been there at the time the ordnance arrived," said the official, who asked not to be named.

Witnesses reported that at least 14 civilians were killed in the bombing that destroyed four houses and left a crater eight meters (26 feet) deep and 15 meters wide.

Major General Stanley McChrystal, with the US Joint Chiefs of Staff, admitted that coalition forces "do not have hard battle damage assessment on what individual or individuals were on site," at the time of the attack.

In southern Iraq, a spokesman for British forces said "a couple more days" were needed before Iraq's second city of Basra could be declared secure, a day after Britain had said the battle for the city was largely over.

While some Basra residents defaced murals of Saddam after the British entered, thousands looted public buildings and homes of Baath party members.

But one Basra resident told AFP: "The people in Basra feel defeated. Sure, we certainly hated Saddam but we also hate the British and Americans."

British spokesman Colonel Chris Vernon said that senior officers had met with an unidentified Iraqi leader to draw up an interim committee to run the city after the collapse of Saddam's Baath party in the city.

In London, a government minister said British forces were holding more than 6,500 Iraqi prisoners of war.

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