Large numbers of U.S. forces supported by helicopters gathered outside this Euphrates River (search) village Saturday, pushing ahead with their region-wide operation to wipe out supporters of Iraq's most wanted militant. The military said four more Marines were killed.

Frightened residents retreated indoors as a large convoy of mainly Marines, backed by tanks redeployed several miles from Rommana to Obeidi, on the northern bank.

Shelling began several hours later, damaging a house in the old part of this village and wounding five people, said Obeidi hospital doctor Saadallah Anad. He said he did not know if U.S. weapons fire hit the house but said helicopters were hovering over the area.

"We are living in a catastrophic situation. We don't have medicines or equipment and we are worried that when our ambulances go out the Americans could strike at them," he said.

The U.S. military said the four Marines were killed when their troop transporter was struck by a bomb near Karabilah, a village near Obeidi and close to the Syrian border. Their deaths brought to nine the number of U.S. casualties in the week-old campaign.

Marine commanders estimated that more than 100 insurgents and foreign fighters have been killed in the campaign, aimed at allies of Abu Musab al-Zarqawi (search). The Jordanian-born militant has claimed responsibility for scores of bombings, ambushes and kidnappings.

The military had no immediate comment on the Obeidi operation, but it appeared to signal a new phase in the high-profile offensive.

Operation Matador was launched last Saturday in several villages close to the Syrian border known as major routes for foreign fighters entering Iraq to battle coalition forces. Residents said U.S. troops blocked the main road linking Obeidi with safer areas to the east outside the field of operations.

"There is fear among the residents of Obeidi, but we don't think it (the village) has any military importance. There are no fighters in the village," said one resident, 35-year-old Khalaf Ali.

The campaign, the largest since insurgents were forced from Fallujah six months ago, has killed more than 100 suspected foreign fighters allied with Jordanian-born militant Abu Musab al-Zarqawi, the military has said. Scores have also been captured.

Al-Zarqawi, a Sunni Muslim terror mastermind, has claimed responsibility for scores of bombings, assassinations and kidnappings in a bid to derail the U.S.-backed, Shiite-led government.

The offensive came amid a surge of militant attacks that have killed at least 430 people across Iraq since the government was announced April 28.

Violence continued Saturday with three Iraqi street cleaners killed when a roadside bomb exploded apparently prematurely in Dora, a southern Baghdad neighborhood, said Dr. Zaid Adil of Yarmouk Hospital.

A suicide bomber detonated his vehicle near an Iraqi police patrol in central Baqouba, north of the capital, wounding three policemen and a civilian, said police Col. Mudhafar Muhammed.

A similar car bomb attack in central Baghdad on Saturday killed at least four Iraqis and injured 11, police said at the scene. The blast outside the former Ministry of Education destroyed cars and set fire to a minibus.

In the northern city of Mosul a roadside bomb killed a 10-year-old boy and wounded two Iraqi soldiers and a policeman on patrol, police Col. Wathiq Mohammed said.

At least nine more Iraqis were killed Friday in a series of bombings, ambushes and other attacks. Also Friday, an American soldier was killed and four others wounded when a car bomb exploded in Beiji, 155 miles north of Baghdad, the military said in a statement.

Obeidi is in Iraq's violent Anbar province, where Iraqi fighters with machine guns and grenade launchers have been setting up checkpoints in recent days, apparently in preparation to do battle. But here the streets were virtually empty Saturday as residents bolted doors, remained inside and waited for a possible U.S. offensive.

Overnight, U.S. warplanes streaked noisily overhead and several loud explosions were heard in various locations throughout the region.

U.S. military spokesman Capt. Jeffrey Pool said Marines are conducting a "cordon and search" operation in Obeidi "looking for insurgents, foreign fighters, weapons and IED making material." He said there were no airstrikes in Obeidi Saturday.

This remote desert region is a haven for foreign combatants who slip across the border along ancient smuggling routes and collect weapons to use in some of Iraq's deadliest attacks, according to the military.

The U.S. military has confirmed five Marine deaths so far and says about 100 insurgents have been killed in the operation.

But a Washington Post reporter embedded with U.S. forces put the American death toll Thursday at seven — six of them from one squad.

At least 1,613 members of the U.S. military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.