As US troops claimed to have seized three presidential palaces, five massive blasts could be heard from the direction of the main complex on the banks of the Tigris, which has been pounded repeatedly since the US-led coalition launched the war March 20 aimed at toppling Saddam from power.

An arms depot had caught fire and thick white smoke covered the Republican Palace. Fuel trenches inside the compound were set ablaze belching out layers of black smoke.

The sound of heavy firing rang out across Baghdad, with shooting from both small and big guns continuing repeatedly. Troops could be seen from the opposite eastern bank of the Tigris moving around the outside wall along the river.

Lieutenant Colonel Peter Bayer, operations officer for the US army's 3rd Infantry Division, said US troops had "secured the main presidential palace" and another palace in the city center as well as a third near the airport.

"There are two palaces (in the city center), we own both of them," Bayer told reporters.

He said they were captured by the division's Second Brigade which sent two tank battalions and a mechanized infantry battalion, totaling some 65 tanks and 40 Bradley fighting vehicles, into the city.

However, AFP correspondents said the administrative district around the palace, including the ministries of information and foreign affairs, were still in Iraqi hands at 10:15 am (0615 GMT).

Iraqi Information Minister Mohammad Said al-Sahhaf told reporters that US forces had been "repulsed".

Heavy explosions had begun booming into the grey skies from around 6:15 am (0215 GMT), apparently from artillery fire to the capital's west -- site of the international airport which was seized by US troops Friday.

There appeared to be a lull in the fighting by 10:00 am (0600 GMT).

On the road leading up to the presidential palace, an Iraqi militia fighter clad in military fatigues and a red keffiyeh headdress stood guard, as others around him armed with Kalashnikov rifles and rocket-propelled grenades stopped cars from approaching at a checkpoint made of sandbags.

Dozens of men in civilian clothing, with ammunition strapped across their chests, stationed themselves behind walls and trees, as ambulance sirens wailed across the city.

As the fighting raged, the streets were deserted except for a few civilians who tried to drive away and nervous-looking militiamen running in all directions.

Some people had stacked mattresses and other coverings into their cars as they tried to find a safer place to stay.

Almost all central shops had downed their shutters and the station for buses heading outside Baghdad was completely empty.

Warplanes had flown over the city all night, sometimes at low altitude, without bombing any targets.

US or British forces have repeatedly rained down missiles and bombs on the Republican Palace, which was built in 1982 and is said to be designed to withstand an explosion the power of the atom bomb that fell on Hiroshima in

Karl Bernd Esser, the German architect who says he designed the bunker buried deep beneath the palace complex, recently told Germany's ZDF television that the walls were three meters (10 feet) thick and could withstand temperatures up to 300 degrees Celsius.

Esser said on his company's Internet website that the bunker has a total area of 1,800 sq meters (19,370 sq feet).

It cost 66 million dollars to build, but proved its worth in the 1991 Gulf war, withstanding aerial bombardment.

The website of the company he works for, Sheltex, shows pictures said to be of a command center in the bunker as well as the presidential bedroom, part of the air-conditioning system and a hideaway.

It said the bunker is capable of holding up to 90 people and could withstand a hit by a conventional 250-kilogram bomb or protect the occupants from the effects of a nuclear, chemical or biological attack.

SPACE.WIRE