United States troops say they are in control of large parts of Baghdad's international airport.
A US tank moves across part of the sprawling airport
Soldiers of the 3rd Infantry Division fought their way into the airport after a heavy bombardment overnight but continued to face Iraqi shelling on Friday morning.
As US forces moved to tighten their grip around Baghdad, US Central Command said three US soldiers were killed when a car exploded at a military checkpoint north-west of Baghdad on Thursday night.
US officials believe the explosion, which also killed the driver and a pregnant woman in the car, was a suicide attack.
As people in the Iraqi capital remained largely without electricity and water after another night of sustained bombing, President Saddam Hussein urged them to defend their city.
In a statement read out on Iraqi television by the information minister, the president vowed to defeat US-led forces.
"We are determined, God willing, to defeat [the invaders] and destroy them on the walls of our capital," he said.
In other military developments:
- US Central Command says it has received reports that about 2,500 Iraqi Republican Guards have surrendered to US marines between Baghdad and Kut, about 170 kilometres (105 miles) away
- Kurdish fighters, backed by small groups of US soldiers, advance towards the northern city of Mosul but meet heavy fire from Iraqi troops, Reuters reports
- Further south, British soldiers continue operations to secure the second city of Basra, establishing what they say is a holding position across the southernmost bridge into the city
Sources say 14 lorries with Iraqi troops sped out towards the airport on Friday morning as panicked residents fled the other way.
"There were planes all night dropping bombs and there was shelling all night," a woman said.
In an assault that began on Thursday evening, US tanks moved along a single-lane road towards the airport with Iraqi fighters firing from all sides for four hours, the Associated Press reported.
The US forces were backed by F-15E and F18 fighter jets which dropped bombs on the airport area, targeting fuel and hangar facilities.
At least 320 Iraqi soldiers were killed in the fighting, US military sources said. There were no reports of American casualties.
"We control the airport. It's a big area with a lot of buildings that need to be cleared but it's ours," Colonel John Peabody of the 3rd Infantry Division told Reuters.
The BBC's Gavin Hewitt, who is with the 3rd Infantry, says although fighting is continuing, the Iraqi resistance has seemed fairly light and not particularly coordinated.
The Iraqi formations they have so far encountered have been small - comprised of about several hundred men.
Early on Friday, US troops fought off an Iraqi counterattack some 20 kilometres (12miles) from the airport, destroying several tanks in a fierce firefight, Reuters reported.
Tough fights ahead
Military analysts say the capture of the airport would both have propaganda value for the coalition and strategic importance as another airstrip to use to bring in supplies.
But General Richard Myers, the top US military officer, warned that there are "still a lot of tough fights
"Nobody should be euphoric that now that we are on the edge of Baghdad this thing is just about over," he said. "That's not true."
HAVE YOUR SAY
This battle will be won by America and its allies at a great cost to innocent Iraqi people
Mohammad Shoaib, New Delhi, India
To the south-east of the capital, US marines are advancing on the south-eastern outskirts of Baghdad after pushing up the River Tigris from Kut overnight.
The BBC's David Willis, who is travelling with them, saw the burned out shells of Iraqi tanks and armoured vehicles lining the road.
Baghdad was plunged into darkness overnight by its first blackout of the war which cut in as the assault on the airport began .
Despite the call to arms by President Saddam Hussein, there remain few defences, no real troop movements and a brittle air of business as usual, the BBC's Andrew Gilligan reports.
However, more families are packing their cars and leaving the city.
In other developments:
The foreign ministers of France, Germany and Russia are due to meet in Paris to discuss the Iraqi crisis
- Iraqi Foreign Minister Naji Sabri responds to speculation about the health and whereabouts of Saddam Hussein, telling the BBC the president is alive and well
- The first major supplies of United Nations food aid into northern Iraq are expected to cross the border from Turkey later on Friday
- Red Cross lorries from Kuwait are carrying medical aid destined for Basra, while UN experts assess humanitarian needs in southern town of Umm Qasr
The US Congress approves $80bn finance for war on Iraq but money earmarked for post-war reconstruction will not go to companies in France, Germany, Russia or Syria