The battle for Baghdad is on. After overrunning patchy resistance from Iraqi forces, US troops are taking up positions outside the Baghdad international airport, which is about 20km from the centre of the city.

According to The Washington Post, the 3rd Infantry Division has approached from Karbala in the southwest, crossing the Euphrates River.

The 1st Marine Expeditionary Force has come from the southeast, passing by the city of Kut, traversing the Tigris River, it said.

Republican Guard units are repositioning, but their motives are unclear, US officials said.

CNN quoted Captain Frank Thorpe, a spokesman for US Central Command, as saying that the ability of the Iraqi leadership to command and control its troops is significantly down.

"The dagger is clearly pointed at the heart of the regime right now," said Brigadier General Vincent K Brooks, another spokesman for the Central Command.

On Wednesday, the US troops said they had destroyed the Baghdad and Medina divisions of the Republican Guard.

"Our land component initiated a two corps attack to destroy Republican Guard positions defending Baghdad. The 1st Marine Expeditionary Force attacked the Baghdad division near the town of Kut. The Baghdad division was destroyed," said Gen Brooks.

Later, a Pentagon spokesman said 5th Corps' 3rd Infantry Division hammered the Medina division near Karbala.

"We've crossed a bridge and are threatening Baghdad," said Colonel Will Grimsley, the division's 1st Brigade commander.

However, Iraqi Information Minister Mohammed Saeed al-Sahaf said, "They are lying every day, they are lying always and mainly they are lying to their public opinion," Sahaf said. "What they say about a breakthrough is completely an illusion."

According to BBC, Iraqi TV carried comments by the commander of the Baghdad division, saying only 17 of his men had been killed.

Gen Brooks claimed that the American troops had crossed a 'red line' around Baghdad amidst fears that the elite units of the Iraqi government could retaliate with a chemical attack.

The US claims that the 'red line', set up by President Saddam Hussein around Baghdad, is the area within artillery and missile range of the Republican Guard units.

In the north, Kurdish soldiers are securing a 13km stretch of road, vacated by Iraqi soldiers, between the towns of Kalak and Mosul.

Meanwhile, President Saddam Hussein appeared on Iraqi TV and said that only a third of Iraq's armed forces have engaged in the war.