Major General Buford Blount, commander of the 20,000-strong Third Infantry Division, said troops of his second brigade controlled a key intersection south of Baghdad.

He said they were 15 kilometers from the city center and "they have the southern access to Baghdad blocked," he said.

Another officer with the same division said lead elements were also in the "neighbourhood" of the capital's main airport, which is some 20 kilometres to the west of the city centre.

"We are in the neighbourhood but we ... have not yet achieved that objective," the officer said.

"I really do not think it's going to be too long."

Captain Frank Thorp, a spokesman for the US Central Command in Qatar, said US troops were in the "vicinity" of Baghdad but he refused to be more specific to protect operational security.

Special forces commandos had also "moved closer" to the capital during the night, he said.

"Overnight we have been able to prevent the destruction of several significant infrastructure facilities such as bridges and a dam," Thorp said, without providing details.

"What we have seen is the ability to move through from our positions of a couple of days ago, with minor damage on our part, and we are now in the vicinity of Baghdad."

Thorp said two Republican Guard divisions, the Baghdad and Medina, were "no longer credible fighting forces" but he admitted the Iraqi troops may have simply fled to fight another day.

"It's a combination of capitulation, being destroyed or hiding, as well as running for the hills or perhaps taking cover for another fight," he said when asked to explain the condition of the Iraqi forces.

"Some of them may have moved into Baghdad as they retreated from the Republican Guard locations but I do not have any reports of great movements into the city."

He said the First Marine Expeditionary Force had entered Al-Kut, around 150 kilometres (90 miles) southeast of the Iraqi capital

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