US-British forces also stepped up their air strikes on the capital a day after coalition forces reported breakthroughs near Baghdad in their drive to unseat Iraqi President Saddam Hussein.

As the war entered its third week, the US army's 3rd Infantry Divsion, backed by the 82nd Airborne Divsion, drove towards Baghdad from the south. US marines moved up from the southeast.

Major General Buford Blount, the commander of the 20,000-strong 3rd Infantry Division, said troops of his second brigade controlled a key intersection south of Baghdad after heavy fighting earlier Thursday.

Blount said his troops were 15 kilometers from the city center and "they have the southern access to Baghdad blocked."

The general said his troops took on elements of the elite armored Medina and Hammurabi divisions of Iraq's Republican Guard that had already been badly hit by days of US air strikes.

"The air force killed most of their tanks before they (US troops) got there," he told AFP.

A senior US officer in Kuwait City said the troops were "in the neighborhood" of the main airport, which is 20 kilometers (12 miles) from the center of Baghdad, and were poised for a strike.

"We have not yet achieved that objective," said the officer, who also spoke on condition of anonymity. But he added, "I really do not think it's going to be long."

Captain Frank Thorp, a spokesman for the US Central Command in Qatar, said special forces commandos had also "moved closer" to the Iraqi capital.

"Overnight we have been able to prevent the destruction of several significant infrastructure facilities such as bridges and a dam," Thorp said, without providing details.

The aerial blitz against Baghdad appeared to be intensifying as dull explosions from the edge of the city continued during the morning after a night of heavy bombardment on its southern and southeastern fringes.

Iraqi Information Minister Mohammed Said al-Sahhaf said the bombings had killed 27 civilians and wounded 193, and he denied US forces were anywhere near Baghdad.

US officers earlier said some 500 Iraqi troops were killed including members of the Special Republican Guard, Saddam's toughest unit, in clashes with US forces for a key bridge some 30 kilometers (20 miles) southwest of Baghdad.

Ferocious fighting erupted by the Euphrates River bridge captured by the Americans on Wednesday and targeted by three Iraqi counter-attacks on Thursday, an AFP correspondent said.

US forces hit back with artillery fire from Bradley armoured vehicles and Paladin guns, as well as from A-10 Thunderbolts which flew overhead.

There was no immediate word on overall casualties among the Americans on Thursday, but US officers said two US soldiers were killed in an apparent Iraqi rocket-propelled grenade attack west of the Euphrates.

The US forward headquarters in Doha said earlier a US F/A 18 Hornet fighter and its pilot, based on an aircraft carrier, had gone down Thursday. It did not confirm television reports the aircraft had been shot down.

A US Army Blackhawk helicopter was shot down Wednesday, but there were conflicting reports on the toll, The Pentagon said seven had died, while the US Central Command said only that six were aboard.

Southeast of Baghdad, US marines supported by renewed air strikes pushed cautiously towards Baghdad from the town of Kut, around 150 kilometresmiles) away. They braced for a decisive battle.

"We have accomplished every objective quickly and easily. I don't think it's a trap by the Republican Guard -- they're still trying to fight but they have no training, poor equipment and they're very sloppy," said Master Gunnery Sergeant Errol Ovid.

Coalition jets and attack helicopters continued to weed out the Iraqi positions in Kut after a pause during the night when, according to one military source here, they "ran out of targets".

In the southern port of Basra, besieging British forces were still facing resistance from around 1,000 Iraqi militia, along with regular troops who have moved back into the city, a British military spokesman said Thursday.

"There are somewhere around a thousand, but it may be more," Colonel Chris Vernon told reporters when asked the size of the irregular forces within the city.

"It's quite clear that elements of (the Iraqi army's) 51 brigade that we gave an opportunity to capitulate have pulled back inside," he added.

WAR.WIRE