"We've crossed a bridge and are threatening Baghdad," said Colonel Will Grimsley, 1st brigade commander of the 3rd Infantry Division.

US forces were now within 50 kilometers (30 miles) of Baghdad, said Major General Stanley McChrystal, vice-director of operations of the Joint Staff, while US sources in the region put them just 30 kilometers (20 miles) south of the city.

The Medina and Baghdad Republican Guard divisions, which were defending the approaches to Baghdad at Karbala and Kut, were effectively destroyed in the fighting Wednesday, McChrystal said in a biefing in Washington.

Lieutenant Colonel Thomas Smith, commander of the 1st Brigade of the 11th Engineering Battalion, said there were Iraqi casualties but did not report any coalition losses after the intense fighting for the key bridge.

The exact location of the bridge was not given, but US military sources said it was 30 kilometers from the capital.

The Iraqis detonated an explosive charge under the 300-yard (metre) bridge over the Euphrates, shattering a concrete beam and a steel girder, Smith told an AFP correspondent travelling with US troops, adding the bridge was still usable.

He explained that as Iraqi artillery rained down on the west side of the river, US soldiers crossed it in rubber boats and attacked the elite Republican Guard units from underneath the bridge.

The bridge was finally seized in mid-afternoon, Smith said, after US Apache helicopters pounded the Iraqi air defence system.

The bridge was captured as part of a major two-pronged ground US assault on Republican Guard divisions defending the approaches to the Iraqi capital.

"The dagger is clearly pointed at the heart of the regime and will remain pointed at it until the regime is gone," Brigadier General Vincent Brooks told a news conference at US Central Command's forward base in Qatar.

Brooks said marines had "destroyed" the Baghdad Republican Guard division, but an Iraqi military spokesman insisted the division "has not suffered any losses and is ready to confront the enemy."

"The Baghdad division maintains its cohesion and has a morale of steel," he told AFP.

An AFP reporter travelling with the US 3rd Infantry Division reported passing through the strategic "Karbala gap" passageway to the west of Karbala, a vital gateway to Baghdad some 80 kilometres (50 miles) to the north.

The 3rd Infantry met only "disorganised" resistance as they drove through the narrow desert strip between the city and a large lake to the west, said first brigade commander Colonel Will Grimsley.

A-10 Thunderbolt planes could later be heard bombing Iraqi positions to the northeast of Karbala as the troops continued to push forward, declining to enter the Shiite holy Muslim city itself.

Marines meanwhile cut off the Baghdad Republican Guard division during a major battle on the approach to Kut after crossing the Tigris, a senior US officer told AFP.

He said Iraqi soldiers were "voting with their feet" and fleeing the US armour as it advanced near Kut, around 150 kilometres (90 miles) southeast of the Iraqi capital.

A 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.

But coalition aircraft were attacking the division as it headed south, he added.

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

"We have only deployed a third of our army, or even less than a third," said the message read on Iraqi satellite television.

In the city of Najaf further south, coalition troops came under fire from the Ali mosque, a revered shrine in Shiite Islam, a US military spokesman alleged.

"We'refusing to return fire at the mosque," Ensign David Luckett added.

Iraqi Information Minister Mohammed Said al-Sahhaf for his part accused the US-led coalition of trying to destroy holy Shiite shrines in Najaf and Karbala.

In Baghdad itself, Iraqi gunners opened up anti-aircraft fire Wednesday night as intensive bombing rocked the outskirts of the city following a day of relentless bombardment that targeted Saddam's main palace compound on the banks of the Tigris.

The new round of bombing began at around 10:00 pm (1900 GMT) and lasted more than 10 minutes, AFP correspondents reported.

Information minister Sahhaf said 10 people had been killed and nearly 90 people wounded in Baghdad on Tuesday, and 14 killed and nearly 100 wounded in other parts of the country.

Fighter jets from the USS Kitty Hawk also pounded an Iraqi intelligence facility in the besieged southern city of Basra with 2,000-pound (900-kilogram) bombs, the military said Wednesday.

And in the north, Kurdish rebels advanced on two roads towards Mosul on Wednesday after Iraqi troops fell back on Iraq's third city overnight.

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