US and UK forces have engaged in fierce fighting in at least three major encounters across southern Iraq as they encounter stiffer resistance than they had been expecting.
UK soldiers have been fighting near Basra in the south
US troops and members of Iraq's Fedayeen units have fought a major battle in the town of Samawah, the site of a crucial bridge on the way to Baghdad.
US forces have also bombed the town of Nasiriya after coming under fire overnight from defenders - as many as 30 US soldiers have been injured, some of them possibly by so-called friendly fire.
And UK tanks destroyed 14 Iraqi tanks and a number of armoured vehicles attempting to break out of the city of Basra.
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Separately, hundreds of American troops have parachuted into northern Iraq in the first big US deployment north of Baghdad - what one unnamed US defence official called "the beginning of the northern front".
The Pentagon said the paratroops from the 173rd Airborne Brigade had taken control of a key airfield in Kurdish-controlled territory, about 50 kilometres (31 miles) north-east of the city of Irbil.
Also in northern, Iraq Kurdish militiamen have crossed the front-line into Iraqi government-controlled territory, seizing a hilltop position guarding the advance to the city of Kirkuk, after Iraqi forces withdrew.
Command sources from the Patriotic Union of Kurdistan (PUK) say hundreds of Kurdish tribesmen have been massacred near Kirkuk, allegedly for refusing to fight alongside forces loyal to Saddam Hussein.
US troops are on the move in northern Iraq
The BBC has not been able verify these reports.
In the fighting in the south, the Americans used heavy guns and tank shells as well as Apache helicopters to try to dislodge an estimated 1,500 Fedayeen fighters guarding a bridge across the Euphrates river.
The US needs to capture the town to secure its supply routes as its forces move north, according to the BBC's Gavin Hewitt, who is travelling with the troops.
In the encounter near Basra, UK Challenger tanks destroyed 14 Iraqi T-55 tanks on Thursday morning.
That engagement follows an overnight encounter in which US and UK air strikes and artillery engaged a column of Iraqi vehicles in the area.
There have also been reports that dozens of US Marines were injured by other American troops in the clashes around the town of Nasiriya.
As many as 37 Marines are believed to have been injured, some critically.
Reports from the area suggest that two US units sent to attack a group of Iraqis firing on them ended up shooting at each other instead of the hostile troops.
On Thursday, Iraqi Health Minister Omid Medhat Mubarak said more than 350 Iraqi civilians had died since the war began eight days ago.
He accused the US of having bombed a shopping area on Wednesday, killing at least 14 civilians in the residential area of Shaab
The US - which says it is doing everything possible to avoid civilian casualties - does not admit responsibility for the deaths.
A US military spokesman at coalition Central Command said: "Our early intelligence report provides no conclusive evidence that we have caused the damage in the civilian marketplace.
"One possibility and high probability is that it was caused from the fallout from the regime's anti-aircraft fire."
But the BBC's Andrew Gilligan in Baghdad says that explanation is "unlikely because we simply haven't heard any anti-aircraft fire in the city for the past four days".
The US military has admitted using precision-guided weapons to target Iraqi missiles and launchers which it says were hidden in a residential area less than 100 metres (300 feet) from homes.
Other military developments
- Baghdad comes under renewed bombardment from coalition war planes, with powerful blasts reported in both the centre and outskirts of the city
- The US says that it will step up operations in the next few days as weather in the region improves after days of sandstorms
- UK raids destroy transmitters in Basra, taking state radio and television off the air in the city and effectively cutting off its communications with Baghdad
- A UK military spokesman says two soldiers missing since Sunday are now believed to have been killed
- The US is sending another 30,000 troops to join the campaign in Iraq
The US Army troops dropped into northern Iraq jumped from low-flying transport planes onto the Bashur airstrip, a reporter from the Philadelphia Inquirer travelling with them said.
More troops and equipment, including tanks and other armoured vehicles, are expected to be flown in soon.
Sandstorms have hampered coalition troops in southern Iraq
The force is smaller and lighter than the US originally hoped.
The US military had hoped to send troops in overland, but failed to reach an agreement with Turkey about using its bases and airspace.
In other developments
- UK Chancellor Gordon Brown announces that he will nearly double the UK war budget to £3bn ($4.5bn)
- The UK says the discovery of chemical weapons protection suits at a deserted Iraqi command post in the south could indicate that Iraq intended to use chemical weapons in the war
- General Peter Pace, vice-chairman of the US Joint Chiefs of Staff, accuses Iraq of executing prisoners of war, though Pentagon sources say they are unable to confirm his comment
- Kuwaiti officials say a Patriot anti-missile battery destroyed a missile fired at Kuwait from southern Iraq
- A UK ship carrying 500 tons of food, water and blankets has been prevented from docking in the port of Umm Qasr by the discovery of a mine in the harbour
- US President George W Bush and UK Prime Minister Tony Blair are meeting at the Camp David retreat in the US to discuss the shape of a post-war Iraq.