"This is it, the last push," said Major Maurice Goins before the advance near the Shiite Muslim holy city of Karbala, some 80 kilometers (50 miles) south of Baghdad.

Members of the 3rd Infantry Division met only "disorganised" resistance as they drove through a 3,000-metre (yard) wide desert strip known as the Karbala Gap, said Colonel Will Grimsley, commander of the division's first brigade.

It was not clear whether any of Iraq's elite Republican Guard were involved in the resistance between the city and a nearby lake.

Elements of the Guard's Medina armoured division and other units had earlier been reported lying in wait in the area but apparently failed to engage in combat.

"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 the gap in an operation which began shortly after midnight (2100 GMT Tuesday).

The advance came after Washington said its troops were engaged in the first major ground battle with Republican Guard forces.

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

US forces were also "very close" to securing the city of Najaf, another 80 kilometers (50 miles) further south, a military commander involved in the operation said, although he added it could still be a matter of days.

In Baghdad itself Saddam Hussein'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 in the latest air raids by the US-led forces.

A series of explosions was heard later at about 6:50 am (0350 GMT) in the southern outskirts of the capital.

Iraqi defence forces, including the Republican Guard, are concentrated in the southern outskirts, preparing to repel a ground attack by US-led troops.

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.

SPACE.WIRE