They said mixed and matched elements of five Republican Guard divisions, elite troops backed by heavy armor, manned a southern arc in front of the capital bracing for a decisive drive to oust President Saddam Hussein.

There was no immediate estimate how many troops this would represent but it could run into the tens of thousands. Iraqi divisions normally comprise 12,000-15,000 troops.

The US army's 20,000-strong 3rd Infantry Division, supported by the 101st Airborne Division and its Apache attack helicopters, is south of Baghdad, geared for an attack with two formations of US marines to its east.

Major John Altman, intelligence officer for the 3rd Infantry Division's First Brigade, said the Iraqis were reinforcing the Republican Guard after days of punishing air strikes and probing ground attacks by US-led forces.

"What's happening is that you reinforce the unit you expect to be in contact and you fill a unit that is attrited," Altman told AFP near Najaf, about 150 kilometers (95 miles) south of Baghdad.

He said the Republican Guard's armored Medina Division had been heavily battered by days of air strikes, artillery attacks and assaults by the tank-busting Apaches.

The Iraqis brought down from north of Baghdad elements of the armored Hammurabi and mechanized Nebuchadnezzar divisions, Altman said. Troops of the Al Nida armored and Adnan divisions were also in place south of the capital.

The intelligence officer said that fighting had been heavy around a bridge that crosses the Euphrates River southwest of the Shiite Muslim city of Karbala 80 kilometers (50 miles) from Baghdad.

"We made great headway," Altman said. "We can easily own the ground there and use the bridge."

SPACE.WIRE