NAJAF, Aug 10: US forces on Tuesday urged civilians to evacuate Najaf on the sixth day of clashes with Shia militiamen that brought a halt to output from Iraq's southern oilfields and sent world prices to record highs.

The occupation troops drove through the centre of the holy city, using loudspeakers to order civilians to evacuate the combat zone immediately and militiamen to leave.

Residents said it was the first time US troops had called for evacuation and feared a massive attack on bastions of the Mehdi Army in the city's huge cemetery and around the mausoleum of Hazrat Ali (AS).

Artillery and tank shells earlier pounded positions in the cemetery. In a possible prelude to stepped up fighting, a senior US military official said on Monday that marines had been given permission by the Najaf governor to enter the shrine to launch an attack.

On Tuesday, the military accused guerillas of kidnapping people and taking them to the cemetery for "torture, execution and burial". "We will not allow them to continue to desecrate this sacred site, using it as an insurgent base of operations," said Col Anthony Haslam, commander of the Marine Expeditionary Unit.

The US rhetoric came one day after radical leader Moqtada Sadr vowed to defend Najaf "until my last drop of blood", rejecting calls from the prime minister for his men to lay down their arms and leave the city.

In the firebrand leader's Baghdad bastion of Sadr City, witnesses said the US military fired a missile into a residential area, destroying an empty house after a patrol came under attack.

Smoke was seen rising from the impoverished neighbourhood as US jets roared overhead in a calculated show of force. Clashes raged for three hours in Sadr City when a US patrol came under repeated attack. The violence was followed by sporadic gun and mortar fire.

As a curfew was imposed from 4pm for a second day running, a Sadr aide called on residents to defend their homes and urged police, security forces and guerillas to join the Mehdi Army in "their fight against the occupation".

"What is going on in Najaf and elsewhere is mass killing by the Americans and the so-called interim government," Qais al Khazali told reporters. The health ministry said that during the day nine people had been killed and 92 wounded in Sadr City, and the southern cities of Basra and Diwaniyah. It was not clear if all the casualties were the result of clashes with Sadr's militia.

CRUDE EXPORTS: Following threats against key oil infrastructure from at least two Sadr aides, the state-owned Southern Oil Company announced on Monday that it was halting the pumping of crude "for security reasons".