U.S. forces adopted a new tactic Tuesday in their sixth day of battles in this city south of the capital, sending patrols armed with loudspeakers into the streets to demand that militants loyal to a radical cleric drop their arms and leave Najaf (search) immediately or face death.

The call, broadcast in Arabic from American vehicles, added a psychological component to the U.S. offensive. It came as U.S. helicopter gunships pummeled a multistoried building 400 yards from the gold-domed Imam Ali Shrine (search) with rockets, missiles and 30 mm cannons — one of the closest strikes yet to what is one of the holiest sites in Shia Islam.

Plumes of thick, black smoke rose from the building, which serves as a hotel for visitors to the shrine. Witnesses said insurgents were firing from inside it and that U.S. forces returned fire.

"We've pretty much just been patrolling and flying helicopters all over the place, and when we see something bad, we blow it up," said U.S. Marine Maj. David Holahan, executive officer of the 1st Battalion, 4th Marines Regiment.

Nearby, Bradley fighting vehicles swept through a huge cemetery, pursuing small pockets of militants hiding in elaborate concrete tombs. Choppers provided support, firing rockets from above, witnesses said.

Sporadic explosions could be heard elsewhere in the city, and Holahan said militants from radical cleric Muqtada al-Sadr's (search) Mahdi Army militia attacked three police stations, two with small arms fire, one with eight mortar rounds.

Despite the violence, Marines said the clashes were much lighter than in recent days — though few expected it to stay that way. "I think it's the quiet before the storm," Holahan said.

Parts of Najaf were deserted, but residents ventured out into the streets, driving small cars nervously along palm-lined roads as eight-wheeled Marine vehicles moved through town on "show of force" patrols.

Residents stood at the gates of their houses, staring. A few children rode bicycles, waving. One U.S. tank stood guard at an intersection in front of a turquoise mosque.

The U.S. military has estimated that 360 insurgents were killed in Najaf between Thursday, when fighting began, and Sunday night, a figure the militants dispute. Five U.S. troops have been killed, along with about 20 Iraqi officers.

The fighting has plagued other Shiite communities across Iraq.

In Baghdad's Sadr City neighborhood, groups of three to five Mahdi Army militants attacked a district council hall repeatedly with mortars, gunfire and rocket-propelled grenades, clashing with U.S. and Iraqi forces, said U.S. Capt. Brian O'Malley of the 1st Brigade Combat Team.

The Health Ministry said the skirmish killed one person and wounded 18. Other clashes in Baghdad killed a second person and wounded 11 others.

There were no employees there during the attacks, and O'Malley said about 14,000 people "haven't been able to go to work since the fighting started" in Sadr City days ago.

The violence has jeopardized Iraq's oil industry.

But production resumed at Iraq's vast southern oil fields after authorities reached an accord with militant Shiites who had threatened to attack the country's vital export pipelines for crude, an Iraqi oil official told The Associated Press late Tuesday.