US and British troops have advanced deep into Iraqi territory.
US and British troops have been trying to secure Iraq's southern oil fields
US Marines reached Iraq's only deep-water port at Umm Qasr in the south-east and raised the US flag, having overcome some early resistance as they crossed the border from Kuwait.
But despite reports of about 250 Iraqis surrendering in the area, correspondents say the Americans are not yet in control of the whole complex and are working their way towards the old port.
British troops say they have taken control of key oil installations on the nearby al-Faw peninsula.
The military successes came as the US-led forces reported their first combat fatality of the campaign - a US Marine killed by gunfire in southern Iraq.
This came hours after eight British and four American servicemen died when their Sea Knight transport helicopter crashed in Kuwait, in what is believed to have been an accident.
Fierce fighting has been reported around the big oil fields in northern Iraq, which US special forces are trying to secure, according to Western intelligence.
The BBC's world affairs editor, John Simpson, who is near the town of Kirkuk, says he has been hearing the sounds of battle, including artillery and anti-aircraft fire, from the direction of the oil fields.
Kurdish fighters say the Americans have bombed an airfield near Mosul - the other large Iraqi city in the northern oil fields area.
Meanwhile, large explosions have been reported from the direction of Basra, 70 kilometres (44 miles) north of the Kuwaiti border.
British Defence Secretary Geoff Hoon said as many as 30 oil wells in the country were on fire.
BBC defence correspondent Jonathan Marcus says the attacks so far have been more graduated than expected.
In other developments:
- A wave of US B-52 bombers takes off from RAF Fairford in England
- The Iraqi news agency says the country's forces have shot down a US or British warplane - a claim denied by the Pentagon
- Patriot defence systems shoot down more Iraq missiles heading for Kuwait
- The opening of Turkish airspace to US warplanes is held up by a dispute over "technical details", despite Thursday's agreement by the Turkish parliament
Anti-war protests continue around the world after more than 1,000 people are arrested at a demonstration in San Francisco
- European Union leaders meet in Brussels for their spring summit to discuss humanitarian aid to Iraq, and its reconstruction
One convoy of US Marines which crossed into Iraq overnight came under fire from Iraqi forces.
The BBC's Adam Mynott, who was travelling with the marines, says the convoy was attacked with small arms fire and missiles just a few yards inside the Iraqi border.
British artillery was called in from northern Kuwait to bombard the Iraqi positions, while the convoy was forced to retreat. It later continued its advance.
One reconnaissance unit is said to have advanced about 200km (125 miles) through open desert to the west of the river Euphrates.
Scores of Iraqi soldiers have been surrendering
Correspondents have reported seeing towering flames and smoke in southern Iraq, but it is unclear whether this is from burning oil wells.
Elsewhere, the marines met little resistance as a long convoy of vehicles, including tanks and artillery, snaked its way across the Iraqi desert.
The Iraqi capital, Baghdad, was tense but quiet at daybreak on Friday, after sustaining two air raids within 24 hours.
President Saddam Hussein and his family were safe in spite of the air raids that had targeted presidential buildings in Baghdad, the Iraqi information minister said, without giving details of their whereabouts.
On Friday morning, two of the three main buildings in the Tigris complex of ministerial offices were reduced to burnt-out shells - not actually in rubble, but completely unusable, says the BBC's Paul Wood in Baghdad.
The strike, which only lasted 15 minutes, appears to have been precise but the Iraqis report that civilians were injured, he says.
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The Iraqi president's main palace and government offices were among targets struck in the second wave of attacks.
The BBC's Washington correspondent Justin Webb says officials there hope Saddam Hussein's power structure has been significantly weakened and his ability to co-ordinate a strong response to the US-led ground attack has been damaged.
In his first public appearance since America launched its first strike, President George W Bush praised the US troops in action, saying: "There's no question we've sent the finest of our citizens into harm's way."