HADITHA, Iraq — About 1,000 U.S. Marines and sailors, joined by Iraqi security forces, sealed off this Euphrates River town yesterday in the second major dragnet for insurgents this month in far western Anbar province.

A Marine, 10 insurgents and two Iraqi civilians were killed in the first day of the offensive, which targeted an insurgency that is believed to be steadily growing in Haditha.

The offensive followed an operation farther up the river near the Syrian border earlier this month in which nine Marines and 125 insurgents were killed.

Violence continued today, when a car bomb exploded in Baghdad near an Iraqi police patrol, killing three policemen and two civilians and wounding 17 bystanders, officials said. Separately, gunmen fired on a group of people walking to work in Baghdad, killing four Iraqis, including a translator working for the U.S. military, police Lt. Hussam Noori said.

In Haditha, 140 miles northwest of Baghdad, the fighting began before dawn yesterday. Gunfire came from three houses in a narrow street, surprising a Marine patrol that was headed for the city's main market nearby, said Maj. Kei Braun, executive officer for Lima Company of the 3rd Battalion of the 25th Marines Regiment.

One Marine was killed and another injured in the firefight, the military said. Six insurgents were reported killed, with four wounded and four detained. Among the insurgents killed was an imam, Ismaeel Abbulah Shesh, who fired on the Marine patrol, the military said.

Cpl. Jeff Hunter, 26, said he and another Marine stormed one house. "It was pretty intense," Hunter said. "It's quite an experience when you see your friend walk through a door and see a muzzle two inches from his chest."

The insurgents apparently commandeered the houses, causing civilians to be trapped.

Hunter said he threw a grenade inside a house and then another Marine threw a second grenade after forces heard a noise in a back room. That room contained about four women and six children; one woman was fatally wounded, the Marines said.

"She just got caught in the cross-fire," Braun said.

Insurgents were killed throughout the day in the offensive labeled Operation New Market, which began with helicopters dropping off forces along the riverbanks and ground units surrounding the town on the remaining three sides.

Marines found that insurgents were using palm groves along the river to bury and hide weapons, said Lt. Col. Lionel Urquhart, battalion commander. Through yesterday evening, insurgents kept firing mortars at U.S. positions.

While 1st Sgt. Tom Sowers and Staff Sgt. Michael Brady were visiting a radio station in Haditha, two mortars missed them by about 175 yards. One hit a home, killing an Iraqi boy, commanders said.

Haditha is considered strategic because there is an oil refinery south of town and a dam a few miles upstream that provides 13 percent of Iraq's power.

Insurgents are thought to travel through the city on their way to Baghdad or Mosul, the Marines said. Jordanian militant Abu Musab al-Zarqawi, who is blamed for major attacks in Iraq, recently has used Haditha as a refuge, the military said.

The town wasn't always the hotbed it is today, but after last year's siege in Fallujah, many insurgents fled upriver to Haditha, said intelligence officer Maj. Plauche St. Romain.

Last year, the Haditha police station was attacked, and insurgents shot police officers who were on their knees.

The Marine Reserves' 3rd Battalion arrived at its camp in the Haditha Dam in March.

In April, the police chief was assassinated, rendering the town without any law officers. Later the same month, 19 fishermen were found dead, shot execution-style, and their bodies were left in a soccer field, said St. Romain.

On May 7, insurgents used the inside of Haditha Hospital for firing positions and launched a car-bomb attack on U.S. forces in front of the hospital, damaging the building and killing three Marines and a Navy corpsman.

The latest mission also marked a stepped-up U.S. effort in working with the Iraqi 7th Reconnaissance unit of the Iraqi Security Forces, and additional Iraqi forces are expected to join the Marines' camp in Haditha Dam.

More than 600 Iraqis and at least 62 U.S. troops have been killed in attacks since the formation of Iraq's new government April 28. At least 1,648 members of the U.S. military have died since the war's start in March 2003, according to an Associated Press count.

Also yesterday

Al-Zarqawi wounded? Insurgents said in interviews and Internet statements that the leader of al-Qaida in Iraq, Abu Musab al-Zarqawi, was struggling with a gunshot wound to the lung, and one of his commanders said al-Zarqawi was receiving oxygen, heightening suspicion that groundwork was being laid for an announcement of al-Zarqawi's replacement or death.

The Jordanian-born guerrilla's fighters and one of his top lieutenants have said he was wounded in an ambush by U.S. Marines and Iraqi forces last weekend around the western city of Ramadi. A U.S. military official, Lt. Col. David Lapan, said yesterday that he had found no record of such an ambush. Al-Zarqawi is the man most-wanted by the United States in Iraq, with a $25 million bounty.

Lights out: Iraq's interior minister was giving awards to 75 members of the Wolf brigade anti-insurgency unit yesterday when the lights went out, a sign of the country's inability to restore basic services more than two years after the fall of Saddam Hussein. Bayan Jabr's assistants were forced to shine a flashlight at the citations for members of the elite unit for their participation in Operation Squeeze Play. U.S. and Iraqi forces have detained more than 420 people since Sunday.

"Nightline" memorial: ABC will devote an entire "Nightline" broadcast Monday to a roll call of U.S. war dead, nearly a year after some political conservatives condemned a similar tribute as anti-war propaganda, the network said Tuesday. As he did last year, "Nightline" host Ted Koppel will recite the names of more than 900 U.S. servicemen and women killed in Iraq or Afghanistan during the past year as a photograph of each is shown on the screen.

Additional information from The Associated Press and Reuters.