The United States meanwhile said it was unsure if an air raid on Monday had killed President Saddam Hussein, while US authorities faced tough questioning over the deaths of three journalists in Baghdad.

The US military said Baghdad was now surrounded and that its forces were in the heart of the city.

Thousands of marines poured in from the east while fresh waves of airstrikes pounded the southern and southeastern fringes of the city.

In the centre, two US tanks moved onto the key Al-Jumhuriya bridge over the river Tigris, sparking exchanges of fire with lightly-armed Iraqis holed up on the east bank of the river.

The bridge is adjacent to the main presidential palace compound which US forces partially occupied Tuesday amid heavy clashes.

Military officials said one US marine was killed and six others wounded in firefights in the Baghdad suburbs.

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

Hundreds of families could be seen fleeing the fighting in the capital in cars, trucks and minibuses.

The heavy fighting also took its toll on the city's hospitals, with international aid agencies warning medical supplies were critically low and hospitals were stretched to the limit because of a large number of civilian casualties.

"The situation in Baghdad is starting to become critical especially with the power cuts," said Nada Doumani, a spokeswoman for the International Committee of the Red Cross (ICRC), adding that the cuts were affecting water supplies.

Though the US military appeared increasingly confident about the military operation, it was unsure of the success of its latest attempt to bomb Saddam and his two sons.

Major General Stanley McChrystal, vice director of operations of the Joint Staff, told a Washington press briefing the air strike on Monday had been "very, very effective," but it was not known if the targets were still alive.

"We do not have a hard and fast assessment of what individual or individuals were on site," McChrystal said.

For its part, Wednesday's British press quoted intelligence services as saying Saddam likely survived the strike.

The Times said Britain's foreign intelligence service, MI6, told the US Central Intelligence Agency it believed Saddam left the targeted building in Baghdad just before it was bombed.

"We think he left the same way he arrived ... either by a tunnel system or by car, we're not sure," a British intelligence source was quoted as saying.

Witnesses said 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 in Baghdad's upmarket Al-Mansur district.

"I don't know whether he survived ... The only thing I know is that he is losing power... Saddam Hussein will be gone," US President George W. Bush said following a meeting with his chief ally British Prime Minister Tony Blair in Belfast, the third in as many weeks.

The US military was forced onto the defensive Tuesday after three journalists were killed in Baghdad by US fire.

Cameramen from the Reuters news agency and Spanish television station Telecinco were killed when a US tank shell hit the Palestine Hotel, where the majority of the international media is stationed.

Three Reuters staff were wounded.

The US military said the tank had fired a single round at the hotel in response to grenade and small arms fire from the building. Journalists there at the time said they had not heard any gunfire come from the building.

And a correspondent for the maverick Al-Jazeera Arabic television network died after the station's offices were hit in a separate attack that the Qatar-based network said was a deliberate US strike.

The Defense Department said the US tank crew had acted in self-defense after being fired on.

The attack brought calls from journalists groups for an investigation and put in question US assertions that US forces were taking utmost care to avoid civilian casualties.

Al-Jazeera's editor-in-chief Ibrahim Hilal urged the US and Britain to help get the channel's reporters out of Baghdad, saying "I believe that none of them is safe any more, whether in Baghdad or the rest of Iraq, even those who are with American troops."

Meanwhile, the Pentagon announced Tuesday that 96 US military personnel have been killed and 155 injured since the war on Iraq began March 20.

Ten others are reported missing in action, including two airmen whose F-15E jet fighter went down over Iraq on Sunday.

It was the second US warplane lost over Iraq in two days, following the announcement that an A-10 Thunderbolt strike aircraft had crashed Tuesday after apparently being hit by a surface-to-air missile over Baghdad.

The pilot was later recovered and evacuated.

Setting his sights on post-war Iraq, George Bush provided some relief to key allies when he pledged at his meeting in Belfast with Blair that the United Nations would have a "vital role" to play in rebuilding the country.

He denied a reported split with Britain over the UN's role in supervising an interim Iraqi government. London wants the United Nations to oversee any interim Iraqi administration while Washington has sought initial US-British military control.

French Foreign Minister Dominique de Villepin expressed satisfaction at the statement on the UN's role.

"France is of course pleased at the stance that has been taken by President Bush and Prime Minister Blair," he told reporters.

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

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.

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.

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