The fighting also saw three journalists killed in the city as a result of US fire, angering media organisations.

US officials said a B-1 bomber dropped four 2,000-pound (900 kilogram) bombs Monday on a building in Baghdad where the Iraqi president and his two sons were thought to have been meeting with senior aides. There was no word on Saddam's fate.

With Baghdad virtually encircled, US Army forces spanned out further in the city while thousands of marines in 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 24-year iron-fisted rule -- amid heavy exchanges of tank, artillery and automatic weapon fire on day 20 of the war.

Two US tanks succeeded in moving north out of the palace and occupying a key bridge over the river Tigris, despite stiff resistance from Iraqi forces encamped on the other side.

The Americans also threw new weapons into the Baghdad fray.

Apache helicopters made their first appearance in the skies over Baghdad and an A-10 Thunderbolt "tank killer" plane attacked the palace compound.

The US military said an A-10 was shot down by a missile and the pilot ejected and was rescue3d, but it was not clear if it was the same aircraft.

The ferocious fighting raised the numbers of casualties among civilians and journalists in the city. A British and a Spanish cameraman were killed and three other journalists wounded when a US tank shelled a high-rise hotel used by the media.

The US military claimed there had been firing from the hotel but journalists in the building strongly denied it.

A reporter for the Al-Jazeera Arabic news network also died and a cameraman was injured after the station's offices were hit in an earlier separate attack that the Qatar-based Arabic news station charged was a deliberate US strike.

The bomber strike Monday that targeted a residential neighborhood of Baghdad where Saddam was thought to be was part of a campaign of increasingly personal attacks targeting him, close aides and symbols of his power.

The US television news channel MSNBC quoted US officials as saying they believed Saddam and his two sons may have been killed. But Pentagon officials would not confirm the report.

"We just don't know who might have been killed," one Washington official said after the assault with four 2,000-pound (900-kilogram) bunker-busting bombs in Baghdad's al-Mansur section.

"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 by a bomb that destroyed four houses in al-Mansur and left a crater eight meters (26 feet) deep and 15 meters wide off a main commercial artery.

It was the second attempt by US forces to kill Saddam with a single blow. The US-led invasion kicked off March 20 with a surprise attack by US F-117 stealth fighters on a Baghdad compound where Saddam and his senior aides were believed to have gathered.

The latest assassination bid came three days after an air raid on the villa of Saddam's notorious aide known as "Chemical Ali" for having ordered a gas attack that killed some 5,000 Kurdish villagers in 1988.

Officials suggested Monday that Ali Hassan al-Majid, Saddam's cousin and long his right-hand man, had been killed in the attack in the southern port city of Basra. But they stopped short of outright confirmation.

SPACE.WIRE