Two officers from the US 3rd Infantry Division, along with dozens of Iraqis, died in the battle for Saddam International Airport, which was renamed "Baghdad International Airport" by its new owners, US commanders said.

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

The chief spokesman for Iraqi President Saddam Hussein warned of a counter-attack involving "martyrdom" -- usually a reference to suicide bombing -- to teach the invaders a lesson.

"It will be a great example to them," said Information Minister Mohammad Said al-Sahhaf. "I mean some kind of martyrdom, and there are very, very new ways which we are going to carry it out."

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, underscoring the seriousness of the regime's threats of kamikaze attacks.

The commander of Britain's forces in the Gulf, Air Marshal Brian Burridge, told BBC the regime could be preparing to strike back with chemical or biological weapons, or from behind a "tide" of human shields.

"He (Saddam) could use a human tide and we had signs last night (Thursday) that there were loudspeakers in southwest Baghdad signalling people should rise up and march on the airport," he said.

Brigadier General Vincent Brooks, at Central Command's Qatar base, said Iraqi troops may be hiding in an underground complex discovered at the airport.

Fireballs could be seen early Saturday from the area as warplanes roared overhead.

Earlier in the night small-arms fire could be heard on the city's streets for the first 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.

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.

But he warned that the battle for control of the Iraqi capital would take time.

"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."

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.

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

Arab news channel 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. She raised a rifle in the air, with the other 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, marines closing on the Iraqi capital from the region of Al-Kut rounded up about 2,500 Iraqi soldiers who surrendered rather than face the US ground onslaught.

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.

Brooks also said coalition forces had "effective control" of roads between Baghdad and Tikrit, Saddam's home town north of the capital. Iraqi television, for its part, claimed US paratroops were forced to flee the area after attempting a landing there.

In the south, British patrols outside Iraq's second city of Basra found a cache of 56 short-range ballistic missiles and four missile launchers, but hundreds of Saddam loyalists remained in possession of the town.

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