The commander of the 101st Airborne Division's Aviation Brigade, Colonel Greg Gass, said Najaf was becoming "more and more secure" to US forces after more than three days of combat for control of the strategically important city.

"The big thing was the reaction from the civilian populace," Gass said. "We had civilians welcoming the soldiers yesterday, clapping and waving and cheering them."

Gass said "hundreds" of local people had responded to the US military advance with warmth.

But it was impossible for AFP correspondents, who are based outside Najaf, to immediately verify Gass's assertions.

Several hundred Iraqi soldiers or militiamen are reportedly holed up near Ali's Tomb, the burial site of the Prophet Mohammed's son-in-law, which is located in the heart of the town.

The tomb is sacred to Iraq's majority Shiite population, who have been persecuted by President Saddam Hussein's predominantly Sunni Muslim regime.

While not commenting on the reported threat near Ali's Tomb, Gass said Najaf would never be completely secure of forces loyal to Saddam.

"There are always going to be many threats as long as we are here," he said. "It's a matter of days before it will be secure."

Gass earlier described the combat around Najaf on Sunday and Monday as the heaviest that his forces had been involved in since the start of the US-led war on March 20.

Infantry troops and Kiowa Warrior helicopters from the 101st have played the leading role in the battle for Najaf, along with armoured and mechanised support from the 3rd Infantry Division, according to Gass.

Two 101st Black Hawk helicopters flew into Najaf's single-strip airfield on Tuesday to deliver a small amount of humanitarian aid as an initial step to try to win over the local Shiite population and undermine Iraqi resistance.

However, those efforts appeared to be undermined the previous day when US soldiers manning a checkpoint close to the city shot up a civilian vehicle that failed to stop on their command, killing at least seven women and children.

Najaf, 160 kilometres (100 miles) south of Baghdad, is a key city in the US military push towards the capital.

Control of the city would allow smoother supply and communication lines, while eradicating a base for Iraqi military operations in the centre and southwest of Iraq.

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