BAGHDAD, Iraq – A Marine amphibious assault vehicle patroling during combat operations in the Euphrates River valley hit a roadside bomb today, killing 14 Marines from the same Ohio battalion that lost six men two days ago. It was one of the deadliest single attacks against American forces in Iraq.

Also, an American freelance journalist was found dead in the southern Iraqi city of Basra, the U.S. Embassy said. Steven Vincent had been shot multiple times after he and his Iraqi translator were abducted at gunpoint hours earlier, police said.

The Marines killed today were assigned to 3rd Battalion, 25th Marines based in Brook Park, Ohio, a Cleveland suburb, according to Gunnery Sgt. Brad R. Lauer, public affairs chief with the unit. A civilian translator also was killed and one Marine wounded.

The battalion has been fighting in the volatile Euphrates Valley in western Iraq to seal a major Syrian border infiltration route for foreign fighters. The Marines launched a series of operations in the region in May and June in hopes of pacifying the area so Iraqi military and civilian forces could assume effective control.

U.S. Army Brig. Gen. Carter Ham, in a news conference today, said American forces were mounting simultaneous assaults on a string of towns along the river to root out insurgents and cut off their freedom of movement. As insurgents resist, the area has become increasingly dangerous.

"This is a very lethal and unfortunately very adaptable enemy we are faced with," Ham said, though he noted that insurgents were not targeting American forces any more than usual.

Today's explosion happened just outside the town of Haditha, 140 miles northwest of Baghdad. The Marines were riding in an amphibious assault vehicle, designed to carry troops from ship to shore and on land. It has a road speed of about 45 mph and can carry up to 25 Marines. It is not as heavily armored as the Bradley fighting vehicles that the Army uses.

The losses came on the heels of the deaths of seven U.S. Marines in combat two days ago in the same operation. One died in a suicide car bombing in Hit, another Euphrates River town. The other six, from the same Cleveland battalion, were killed Monday in Haditha while on sniper duty.

The extremist Ansar al-Sunnah Army claimed responsibility for killing the six. Masked gunmen showed up in the Haditha public market Monday afternoon displaying helmets, flak jackets and other equipment they said were taken from the Marines' bodies.

One of the six, Lance Cpl. Jeff Boskovitch, 25, was an aspiring police officer who planned to set a wedding date with his girlfriend when he returned home this fall. He joined the Marine reserves in 2000, his uncle Paul Boskovitch said Tuesday.

"We got a lot of e-mail from him," Boskovitch said. "He felt he was making a difference there and that the Iraqi people were appreciative of what they were doing.

At least 1,820 members of the U.S. military have died since the Iraq war began in March 2003, according to an Associated Press count. The latest deaths come as the Bush administration is talking about handing more security responsibility to the Iraqis and drawing down forces next year.

At least 39 American service members have been killed in Iraq since July 24 — all but two in combat. In addition, the Iraqi Defense Ministry said that since the beginning of April, more than 2,700 Iraqis — about half of them civilians — had been killed in insurgency-related incidents.

The slain journalist, Steven Vincent of New York, had been in Basra for several months working on a book about the city's history. Five gunmen in a police car abducted him and his female translator at gunpoint Tuesday evening as they left a currency exchange shop, police Lt. Col. Karim al-Zaidi said.

In an opinion column published July 31 in The New York Times, Vincent wrote that Basra's police force had been heavily infiltrated by members of Shiite political groups, including those loyal to radical cleric Muqtada al-Sadr.

He quoted an unidentified Iraqi police lieutenant as saying that some police were behind many of the assassinations of former Baath Party members that have taken place in Basra. He also criticized British forces for failing to curb the infiltration.

His body was discovered on the side of the highway south of Basra later. He had been shot in the head and multiple times in the body, al-Zaidi said.

Vincent had kept a Web log about his experiences in Basra, with the entries written as letters to his wife, Lisa.

As he mulled the relationship between democracy, the Middle East and the war in Iraq, Vincent was at times cynical but more often cautiously optimistic and determined to find signs of hope and progress among the Iraqis he interviewed and befriended.

In an entry from June 12, 2005, he wrote: "The people here desperately need — and deserve — law and order, a sense that justice can prevail against malevolent powers stalking their nation."

According to the New York-based Committee to Protect Journalists, at least 46 journalists and 20 media support workers have been killed covering the war in Iraq since March 2003. Insurgent actions are responsible for the bulk of deaths.

The Vienna, Austria-based media watchdog International Press Institute condemned Vincent's killing and urged Iraqi authorities to conduct a speedy and thorough investigation.

The death underscored how "Iraq continues to be the most dangerous country in the world in which to work as a journalist," the group said.