But soldiers from the US 3rd Infantry Division at the airport just outside Baghdad were prepared for a counter-attack after President Saddam Hussein's regime warned of a "not conventional" assault during the night.

Fears of more suicide attacks grew when US Central Command announced that three US soldiers and two civilians had died in a suspected suicide car bombing north of the capital on Thursday night.

Mortar and small-arms duels continued in a corner of the airport, 20 kilometers (12 miles), from central Baghdad hours after US troops and armour smashed through the perimeter fence.

Brigadier General Vincent Brooks, at Central Command's Qatar base, said Saddam's name had been dropped and that the facility was now to be known as "Baghdad International Airport".

Relatively lightly armed Iraqi troops put up determined but ineffective resistance throughout the day.

Two US officers died in the battle, one by mortar fire and another during a gunfight on the periphery of the complex, according to Colonel Will Grimsley. Dozens of Iraqi soldiers are also believed to have perished.

Another US soldier was killed on Thursday alongside a Washington Post journalist when their Humvee all-terrain vehicle plunged into a canal while evading Iraqi fire on the approach to the airport, Grimsley added.

Brooks said an underground complex was discovered at the airport that could be hiding more defenders.

Deeper inside Baghdad, an AFP reporter said small-arms fire could be heard on the city's streets around 6:50 pm (1450 GMT) for the first time since the war to topple Saddam was launched on March 20.

US officers at Central Command, who never comment on ongoing operations, said they had no information about any raids inside Baghdad although special forces troops have reportedly moved into the capital.

Artillery rounds and a missile were also heard hitting the city late Friday, minutes after US-led coalition aircraft pounded targets to the southeast. One plane drew heavy Iraqi ground fire around 10:30 pm (1830 GMT).

Overnight coalition bombing of Baghdad plunged the capital into a seemingly intentional power blackout that cut water supplies for the first time in the war. Supplies were restored to parts of the capital Friday night.

Brooks refused to be drawn on the Pentagon's strategy to take Baghdad, which was at the centre of a steadily constricting noose of coalition ground forces, its defenders battered by non-stop air attacks.

"We will be very deliberate about how we do our work regarding Baghdad," Brooks said, declining to set a timetable for an assault on the city. "It will take time to gain a degree of control and security over ... all of Baghdad."

He added: "We have penetrated the defensive ring that was set by the Republican Guard forces."

The Iraqi regime tried to fight back any way it could. Saddam exhorted his people to resist the invaders in a television address to the nation, but Pentagon officials said the tape was "insignificant".

"Hit them with the power of faith wherever they come near you, and resist, O brave inhabitants of Baghdad," he said. "God willing, you will be victorious and they will be defeated."

Iraqi Information Minister Mohammad Said al-Sahhaf warned there would be a "not conventional" assault on US troops at the airport, who he claimed were "isolated" and facing military disaster.

"It will be a great example to them," he said. "I mean some kind of martyrdom, and there are very very new ways which we are going to carry it out."

The Iraqi regime also claimed that the car bomb explosion which that three US soldiers at the Hadithah dam, 200 kilometres (120 miles) northwest of Baghdad, was the work of two female "martyrs".

The Arab satellite television Al-Jazeera later broadcast testimonies of the two women identified by Iraq's official news agency.

"I vow ... to be a suicide bomber who will defend Iraq," said one of the women, named as Nur al-Shammari. She raised a rifle in the air, with her other hand placed on a Koran, the Muslim holy book.

Coalition forces were controlling a checkpoint 18 kilometers (11 miles) from the dam when a vehicle drove up and a woman, apparently pregnant, stepped out "screaming in fear," Central Command said.

As soldiers approached, the vehicle exploded. The woman and the car's driver were killed along with three coalition troops. Two other soldiers were injured.

The Pentagon has not described the incident as a suicide attack, but Brooks said: "These are not military actions, these are terrorist actions."

To the southeast of Baghdad, US forces said around 2,500 Iraqi troops were taken prisoner after giving themselves up to marines who were closing on the Iraqi capital from the region of Al-Kut.

Brooks also said US special forces discovered what they believed was a "training school" for nuclear, chemical or biological warfare in the west of the country.

Bottles labelled with chemical agents were discovered, but initial investigations did not suggest it was a site for the manufacture or storage of Iraq's alleged weapons of mass destruction, he said.

Meanwhile, in the north, Kurdish fighters backed by US special forces crossed a key bridge on the road to the oil-rich city of Mosul after meeting their first significant resistance from Iraqi forces.

"We will continue to advance, the capture of Mosul is a matter of days, not months," Kurdish commander, Serbast Babili, told AFP.

Brooks also said coalition forces had "effective control" of roads between Baghdad and Tikrit, Saddam's home town north of the capital and a major centre for the Iraqi regime.

In the south, British patrols outside Iraq's second city of Basra found 56 surface-to-surface short-range ballistic missiles and four missile launchers.

WAR.WIRE