But three US soldiers were reported killed in another suspected suicide attack using a car bomb, which also killed two Iraqis in what a senior US commander called a "terrorist" action.

Mortar and small-arms duels were continuing in a small corner of Saddam International Airport, hours after troops of the army's 3rd Infantry Division smashed through the perimeter fence, meeting little initial resistance.

Fighting flared up around 7.30 am (0330 GMT) shortly after the US forces said they had seized around 80 percent of the airport. It did not prevent them searching buildings, clearing bunkers of munitions and preparing the bomb-cratered runway for use by aircraft of the US-British coalition.

But Iraqi troops were feared to be still lurking in a suspected underground tunnel complex.

On the way to the airport the US forces had destroyed two Iraqi T-72 tanks with missiles, Captain Darrin Theriault told AFP.

The mass surrender took place as the marines moved northwards from the town of Al-Kut towards the capital, Navy Captain Frank Thorp said at the US Central Command's forward planning base in Qatar.

"This is the First Marine Expeditionary Force taking on the Baghdad Divsion of Republican Guards," he said.

Colonel Will Grimsley, commander of the 3rd Infantry Division's 1st Brigade, said two American soldiers sustained shrapnel wounds in the fighting but there were no reported US fatalities.

He would only say the number of Iraqi casualties was "high" after witnesses reported earlier that dozens of Iraqis had been killed.

Later, Brigadier General Vincent Brooks announced at Central Command (Centcom) headquarters in Qatar that the airport had been renamed Baghdad International Airport, "and it is a gateway to the future of Iraq."

Brooks also said US special forces had discovered what they believed was a "training school" for nuclear, chemical or biological warfare.

Bottles labelled with chemical agents were discovered at the building in western Iraq during a raid, but he said initial investigations did not suggest it was a site for the manufacture of weapons of mass destruction.

Overnight coalition bombing of Baghdad plunged the capital into into a seemingly intentional power blackout that caused a cut in water supplies for the first time in the 16-day-old war to topple Saddam's regime.

But life in the city center still had a semblance of normality Friday, with cars and public buses on the streets alongside a deployment of armed security and police forces.

With coalition forces making headway against his power base, President Saddam Hussein called on Baghdad residents to "resist the invading forces".

"When the capital resists, the invaders can no longer advance and have to retreat," Information Minister Mohammad Said al-Sahhaf quoted the president as saying in a speech which claimed God was on the side of the Iraqis.

The speech, the latest in a series of calls for Iraqis to fight in recent days, also said they were determined to defeat the forces which have massed "at the doorstep of our capital".

"Fight day and night, hit them without respite," said Saddam, whose recent non-appearance on state television has sparked speculation as to his whereabouts.

Meanwhile, three US troops, a pregnant woman and her driver were reported killed in a car explosion at a US checkpoint in central Iraq.

A Centcom statement did not call Thursday night's explosion a suicide bombing, but Brooks said later, "These are not military actions, these are terrorist actions."

The circumstances were similar to those of a car bomb blast on March 29, which Iraq said would be followed by others against US and British troops.

Coalition forces were controlling a checkpoint 18 kilometers (seven miles) from Hadithah Dam in Iraq when a vehicle drove up and a pregnant woman stepped out "screaming in fear," the Centcom statement 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.

In the north, Kurdish fighters seized a bridge Friday near the strategic northern junction of Khazer after more than 24 hours of fierce fighting with Iraqi troops.

Khazer and its Manquba bridge are strategic points in the advance on Mosul, a majority-Arab city of 1.5 million in a mostly Kurdish area some 400 kilometers (250 miles) north of Baghdad.

SPACE.WIRE