A roadside explosion outside the Iraqi capital on Sunday killed six American soldiers and a civilian journalist, the military said, among 12 U.S. troop deaths reported on a day when two car bombs killed at least 44 Iraqis at a Baghdad market and a police headquarters.

A car bomb in the capital, where U.S.-led forces are in the midst of a crackdown on sectarian violence, killed at least 30 Iraqis. At the police headquarters in Samarra, a volatile city in the Sunni heartland 60 miles north of Baghdad, a car bomb and shooting attack killed 12 police — including the police chief.

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American soldiers racing to the headquarters to help also came under attack by small arms fire and rocket-propelled grenades that left two soldiers wounded, the military said.

Dozens of Al Qaeda linked insurgents — some wearing masks and carrying video cameras and black banners — also paraded through the streets in Samarra, arriving in about 40 cars, in a show of force against the U.S.-Iraqi efforts to tame the Tigris River city.

It was a bombing in Samarra that devastated the golden dome of the Shiite mosque on Feb. 22, 2006, that has been blamed for setting off a cycle of retaliatory sectarian violence that U.S.-Iraqi forces are struggling to curb.

Roadside bombings proved deadly for U.S. forces on Sunday. One in Diyala province killed six Task Force Lightning soldiers and a journalist accompanying them. Three soldiers were killed in separate roadside bombings — two others on Sunday and one on Friday, the military said.

Two Marines were killed Saturday in combat in Anbar province, a Sunni insurgent stronghold west of Baghdad, the military said, and a soldier died Sunday in a non-combat related incident.

The deaths raised to at least 3,373 members of the U.S. military who have died since the Iraq war started in March 2003, according to an Associated Press count.

Britain on Sunday said one of its soldiers died of injuries from a Thursday roadside bomb in the southern city of Basra.

The market blast Sunday erupted about noon in the mixed Sunni-Shiite Baiyaa neighborhood and devastated the area, reducing cars and trucks to their charred skeletons and ripping the roofs and exteriors off shops. In addition to the dead, dozens of others were injured.

Blood pooled in the dirt streets. Hospital officials said two pickup trucks filled with body parts were brought to the morgue.

"I was waiting near a shop to lift some boxes, when I saw the owner of the shop fall down," said Satar Hussein, 22, a worker in the market. "I helped him inside the shop, but he was already dead. The next thing I felt was pain in my left shoulder and some people rushing me to the hospital."

Ali Hamid, 25, the owner of a food store, said he was selling boxes of Pepsi when he was hit with shrapnel in his hand.

"I fainted, and the next thing I remember is some people putting me in a pickup with two dead bodies and rushing me to the hospital," he said, condemning the attack as "a terrorist act aiming at creating more sectarian tension and strife."

No one immediately claimed responsibility for the attack in Baiyaa, the scene of frequent sectarian violence including a bombing and mortar attack last week that killed seven people.

U.S. and Iraqi forces raided the Shiite neighborhood of Sadr City early Sunday, uncovering a weapons cache including powerful roadside bombs that have been linked to Iran, a torture room and killing at least eight insurgents in a gunbattle, the military said.

U.S. military spokesman Maj. Gen. William Caldwell said the target was a Shiite extremist cell that was helping to smuggle explosively formed penetrators, or EFPs, which are capable of piercing armored vehicles.

"Intelligence reports indicate that the secret cell had ties to a kidnapping network that conducts attacks within Iraq as well as interactions with rogue elements throughout Iraq and into Iran," he said.

In one of the buildings they searched, the forces uncovered a large cache of weapons, including more than 150 mortar rounds, and a torture room, replete with several sets of handcuffs and a mask, he said. Soldiers decided to destroy the building rather than risk moving the explosives and accidentally setting them off, he said.

"The extensive damage it would have done in killing innocent civilians in Sadr City would have been horrific," he said.

Footage taken by AP Television News, showed the building reduced to piles of brick and rubble.

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