AMERICAN troops stormed into the heart of the Iraqi capital Baghdad today, seizing Saddam Hussein's new presidential palace on the River Tigris in "a dramatic show of force".

US tanks also ringed the Information Ministry and Al-Rashid Hotel. More than 70 tanks and 60 Bradley fighting vehicles took part in the raid as tank-killing A10 Warthog planes and pilot-less drones prowled the smoke-wreathed sky.

The Pentagon said the incursion was a "show of force" designed to send a powerful message to Saddam Hussein's regime, but it was not necessarily the long-awaited "battle for Baghdad".

Four or five marines were killed when their armoured troop carrier took a direct hit from an artillery shell at a bridge over a canal on the outskirts of Baghdad, said Lt Col BP McCoy of the 3rd Battalion, 4th Marines.

About half-an-hour later, marines swarmed across the bridge into the capital on foot, meeting little resistance.

Also, a group of US armoured personnel carriers in southern Baghdad was hit by rockets, according to field reports. Six American soldiers were reported missing and a large number wounded.

Tanks of the 2nd Brigade of the US 3rd Infantry Division barrelled into the capital on the west side of the Tigris at 6am local time.

A defiant Iraqi information minister declared: "I reassure you Baghdad is safe.

"They are beginning to commit suicide at the walls of Baghdad," Mohammed Saeed al-Sahhaf said in a hastily called press conference on the roof of the Palestine Hotel.

There was no estimate of Iraqi casualties. But US military officials said about 100 Iraqis in military uniform had been killed earlier in the day in a fight at Baghdad's airport after a seven-hour exchange.

The US Army columns moved north-east to the newest and main presidential palace on the river, which divides the capital.

The palace, which is near Saddam Hussein's Ba'ath Party headquarters, was apparently mainly residential rather than used for administrative purposes. Iraqis - some nearly naked - fled along the river banks nearby. Some jumped into the water. An ammunition depot across the river was on fire.

Before the Americans seized the complex, Iraqis shot small arms fire at them from a clock tower overlooking the compound. Tanks quickly destroyed it.

Most of the palace compound was severely damaged from earlier US air raids.

One jubilant US soldier declared: "This is history."

Inside the bombed-out palace, troops from Attack Company, 3rd Battalion, 7th Infantry, rifled through documents and inventoried the building. Some rooms had spectacular river views. A thick layer of dust covered gilded, imitation French baroque furniture. The main palace building - sand-coloured brick ornamented with blue tile - was flooded in the basement and first floor. The rest of the building appeared to be destroyed, hit by cruise missiles or laser-guided bombs. Palace curtains were strewn over the ground, blown from their windows by the explosions.

The assault on Baghdad followed a weekend of incursions by US forces in tanks and armoured cars. Troops rolled through the streets of the capital "destroying all of the enemy vehicles and personnel with whom they've come in contact," said Gen Peter Pace, vice chairman of the US Joint Chiefs of Staff.

Intermittent explosions were heard in the city last night and into today, along with periodic anti-aircraft fire. Shortly before dawn, aircraft could be heard over the capital and heavier explosions shook buildings in the centre, echoing from the southern outskirts.

Iraqi satellite television yesterday showed brief footage of a smiling Saddam in military uniform chairing a meeting it said was held yesterday with his top aides.

British tanks have entered the centre of Basra, Iraq's second city, today, a military source said.

The Desert Rats' armour met "patchy" resistance as the troops moved in from the south-west. The source, at Central Command in Qatar, said there was some "stiff fighting" early this morning.

The tanks, which have been waiting outside Basra for nearly a fortnight, pushed their way towards the heart of the city. The breakthrough came after troops encircling the city pushed forward early today between two and three miles from just north of a bridge marking the southern boundary.

Earlier British tanks and American Cobra helicopter gunships repeatedly pounded a factory complex as Iraqi militiamen responded with machine-gun and sniper fire.

To the north, Americans and Kurdish fighters took up positions in the no-man's-land south of the Kurdish autonomous region. It was reported that the 2nd Battalion, 8th Marines south of Baghdad made an extraordinary discovery - 120 bunkers full of ammunition from Russia, Jordan, Egypt and the United States, evidently from when America backed Iraq in its war with Iran in the 1980s.