A spokesman with the US Central Command told AFP 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 Iraqi President Saddam Hussein'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."

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 teleivision.

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.

SPACE.WIRE