Marines battled guerrillas wearing black fatigues or civilian clothes, with their faces shrouded by headscarves after tanks, amphibious assault vehicles and Humvee jeeps rolled into the western Iraqi town at 1:00 amMonday).

The force, backed by AC130 gunships and Cobra helicopters, took six hours to take control of the industrial area on the town's southeastern outskirts amid sporadic attacks by insurgents firing mortars and assault rifles from rooftops, said Lieutenant Colonel Brennan Byrne.

All day long the sound of mortar rounds and machine-gun fire shook the city as the insurgents ran in packs of four or five, materializing out of alleys and on roof tops, spraying bullets and shooting off rocket-propelled grenades (RPGs).

"We are prepared for every Jihadi and foreign fighter. We are going to drive these guys out and break their backs," said Byrne.

The operation, dubbed "Vigilant Resolve", involves two marine battalions, or more than 2,000 troops, based near this Sunni Muslim stronghold that has been a bastion of anti-US insurgency virtually since the ouster of Saddam Hussein's Sunni-dominated regime a year ago.

Several guerillas were killed. The marines also captured (eds: correct) around 15 insurgents, two of them Sudanese fighters, said Byrne.

A gun-making factory was discovered inside the building where the Sudanese had opened fire on US troops, he said.

A Palestinian was detained but was still being interrogated to determine if he was a so-called foreign fighter.

Three US soldiers were also wounded in an ambush, another marine officer said.

"Right now there is contact in four or five places," he added.

The officer said he could give no estimate of rebel losses as the insurgents were dragging away their casualties.

Cobra helicopters and A130 gunships sprayed fire at the rebels. Children cursed the US marines and erected barricades to support the insurgents.

The troops entered homes where insurgents were believed to be hiding and made some arrests, finding hot rifles tucked under beds, officers said.

Some of the worst fighting occurred early Monday when marines set up a checkpoint at the northeastern edge of the city. The Americans were hit by mortar, rocket-propelled grenade and small-arms fire simultaneously, an officer said.

During the operation, the vehicle of Colonel John Toolan, the marines' 1st Regiment commander, came under fire from a car.

A US helicopter gunship fired on the vehicle, killing all its passengers, Byrne said, without specifying their number. Four to five others were gunned down by the gunship.

"The plan is not to go house to house, street to street. We are trying to get insurgents," Captain Ed Sullivan told AFP.

"There have been doubts that we couldn't walk the street and we can," he said defiantly, in an apparent response to insurgent boasts that US forces were running scared after the contractors' gruesome killing.

The four Americans, who were escorting a truck supplying food to a nearby US military base, were ambushed by gunmen in Fallujah March 31.

The charred corpses of two of them were hacked to pieces in scenes which shocked US public opinion and sparked promises of an overwhelming riposte from Washington.

Monday, five US marines were killed and eight wounded in separate attacks around western Iraq.

One marine was killed when gunmen opened fire on his checkpoint at dawn, prompting US troops to retaliate and inflict an unknown number of casualties among the insurgents, the US military said.

Eight marines were wounded and hospitalised after a mortar attack on their checkpoint to the northeast of Fallujah, an officer said.

"Four (more) marines serving with the 1st Marine Expeditionary Force were killed as a result of enemy action in Al-Anbar province (around Fallujah) on April 5 while conducting security and stabilization operations," the US army said.

The marines died in a bomb blast as they patrolled the village of Zainah south of Abu Gharib prison, one of Iraq's largest jails located between Fallujah and the capital.

They had been looking for hideouts where rebels fired mortars and rockets on the prison.

The deaths raised to 614 the number of US soldiers killed in action in Iraq since last year's US-led invasion.

WAR.WIRE