The US-led invasion force, which crossed the Kuwaiti border overnight, is facing some stiff resistance in southern Iraq.

According to British Defence Secretary Geoff Hoon, parts of the Iraqi leadership are breaking down but resistance against US-led troops remains.

"We are seeing significant signs of a breakdown in the organisation of Iraqi leadership elements at the centre," Hoon told BBC .

"On the other hand, we are still seeing resistance in the south. It is a mixed picture."

British troops have been fighting to capture the strategically important al Faw peninsula in south-eastern Iraq after a sea and air assault in the second day of the war.

But they faced "strong resistance" at Umm Qasr, a deep sea port, as they pressed north towards the southern Iraqi city of Basra.

Port city captured

Hoon said the Iraqis are "not simply giving up in the way that some commentators have suggested that they would."

British soldiers have secured a number of oil fields in the al-Faw peninsula while US troops have captured Umm Qasr.

US marines, who are under British command, took at least 250 Iraqi prisoners.

Colonel Steve Cox told Reuters o­n board the British flagship Ark Royal in the Gulf that the Iraqi troops had surrendered to the US 15th Marine Expeditionary Unit by noon.

The report said the marines raised the Stars and Stripes over Umm Qasr, which is Iraq's main port for cargo. Its capture gives the British-led brigade control of virtually all access to Iraq by sea.

'Three or four days'

In separate assault, a convoy of US Marines which crossed into Iraq came under fire from Iraqi forces just yards across the border.

According to BBC 's correspondent Adam Mynott, there had been much stronger resistance in this sector of the battlefield than many in the US-led forces had expected.

Mynott, who was with the convoy, reported that British artillery was called in from northern Kuwait to bombard the Iraqi positions as the convoy was forced to retreat.

Fierce fighting was also reported in the northern Iraqi city of Kirkuk where US special forces were believed to have been parachuted in to secure the oil fields there.

Elsewhere, US troops met little resistance as another convoy of tanks and other military vehicles cutting across the Iraqi desert towards Baghdad.

A spokesman for the British forces in Persian Gulf said that US-led forces may enter Baghdad within "three or four days".

Saddam 'safe'

In Baghdad, Information Minister Mohammed Saeed al-Sahaf told a news conference today that Iraqi President Saddam Hussein had survived US air raids.

"They targetted the houses of Saddam Hussein and his family, but they are safe. They are safe," said the minister.

A Reuters report said Mohammed Saeed also branded US President George W Bush as the "leader of the international criminal gang of bastards."

This is the first official Iraqi response to the invasion launched by US and British forces, which began yesterday morning with a volley of missiles fired into the Iraqi capital.

Pentagon officials said the strikes were a "decapitating" exercise aimed at eliminating Saddam and other key leaders.

Responding to the US invasion, the information minister said: "We will not let them leave the swamp they have entered. They will meet their fate."

First combat casualty

Meanwhile, CNN television said a US marine has been killed in action, which could be the first combat casualty among the coalition forces.

"One US marine has been killed in the line of fire," said the CNN announcer said, adding there were no further details. The death was later confirmed by an official in Washington.

Earlier today, eight British and four US soldiers were killed in a helicopter crash in Kuwait.