A spokesman with the US Central Command told AFP that the Baghdad, Medina and Nebuchadnezzar divisions were being engaged by US troops south of the capital, while the Adnan division was being attacked from the air to the north.

"We are attacking regime Republican Guard forces in the vicinity of Karbala with elements of 5th Corps, which is the 3rd Infantry Division and 82nd Airborne divisions combined," the official said, requesting anonymity.

"They are attacking in concert with the 1st Marine Expeditionary Force which is attacking near Al-Kut.

"The Baghdad, Medina and Nebuchadnezzar divisions are being engaged south of Baghdad."

The CentCom official said troops from the Adnan division, based in Saddam's heartland of Tikrit to the north of Baghdad, were rushing to support its sister divisions to the south.

"Coalition aircraft are interdicting the Adnan division as it goes south from Tikrit to Baghdad to reinforce," he said.

"Coalition aircraft also continue to strike regime leadership, fielded forces, and command and control targets across Iraq."

An AFP reporter travelling with the 3rd Infantry earlier reported passing through the so-called Karbala gap to the west of the city, a strategically vital passageway for any advance on Baghdad.

"This is it, the last push," said Major Maurice Goins before the attack near Karbala, some 80 kilometres (50 miles) south of the capital.

They met only "disorganised" resistance as they drove through the narrow desert strip between the Euphrates and a large lake east of the city, said Colonel Will Grimsley, commander of the division's first brigade.

"It's much less worrying now we are through the gap," Grimsley said as the troops continued their push north, without entering the city itself.

At least a dozen prisoners of war could be seen huddled to the ground guarded by US soldiers as a convoy passed through in an operation which began shortly after midnight (2100 GMT Tuesday).

General Richard Myers, the chairman of the Joint Chiefs of Staff, had earlier said attacks from the air and ground had reduced the combat capability of two Republican Guard divisions by more than half.

However a message issued in the name of the Iraqi president Wednesday, insisted that the regime had so far committed just a "third" of its forces at most to the fighting against coalition forces.

"We have only deployed a third of our army, or even less than a third," said the message read for Saddam by an announcer in military uniform on Iraqi satellite television.

In Baghdad itself Saddam's presidential compound in the centre of the capital came under intensive attack from coalition bombs Wednesday and the western edge of the city was also pounded, an AFP correspondent reported.

The compound came under fire around 3:05 am (0005 GMT), some 10 minutes after a bridge in the east of the city was targeted, and again just after 1:30 pm (1030 GMT).

A series of explosions was also heard at about 6:50 am (0350 GMT) in the southern outskirts of the capital where the Republican Guard divisions are believed to be massed.

Fighter jets from the USS Kitty Hawk also pounded an Iraqi intelligence facility in the southern city of Basra with 2,000-pound bombs, the military said Wednesday.

F/A-18 Hornets and F-14 Tomcats dropped a total of 16 bombs against the facility on Tuesday, Lieutenant Brook Dewalt told reporters aboard the aircraft carrier. He said the bombs were largely satellite-guided weapons but also included some guided by laser.

British forces have surrounded Basra for around a week but have yet to enter the city.

The commander of British armed forces in the Gulf said the war was now entering a "decisive phase.

Asked if he thought the war, which goes into its third week Thursday, was entering a "decisive stage," Air Marshall Brian Burridge promptly replied: "Oh, sure".

"The point I would make, though, is that decisive phases often take time, so I wouldn't want to give the impression that within a day or two this is going to be finished," he told the BBC.

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SPACE.WIRE