A series of car bombs struck mostly Shiite areas in Baghdad on Wednesday, killing at least seven people and wounding more than 20 as sectarian violence was unrelenting a day after bombers and gunmen struck Shiite worshippers on their most important holy day.

In the deadliest violence Wednesday, two parked car bombs struck simultaneously in separate areas in Baghdad, killing at least six people and wounding 15.

One of the blasts was targeting a transit area in central Baghdad where people can catch minibuses to predominantly Shiite neighborhoods, including the sprawling Sadr City slum. The attack occurred at 12:45 p.m. on the Jamhuriyah Street near the busy Shorja market, killing four people and wounding 12 others, police said.

Shorja, one of Iraq's largest markets, has been struck frequently by bombings, including one on Nov. 21 that killed 25 civilians.

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Another car packed with explosives blew up in the religiously mixed neighborhood of Maamoun in western Baghdad at about the same time, killing two civilians and wounding three others, police said, adding the target of the attack was not immediately known.

Insurgents have launched several bombings in the capital in recent weeks as they seek to maximize the number of people killed before U.S.-Iraqi troops launch a neighborhood-by-neighorhood sweep of the city of some 6 million people. Iraqi authorities have promised to crack down on Sunni insurgents as well as Shiite militia violence that has spiraled since the Feb. 22 bombing of a Shiite shrine in Samarra.

A car bomb also struck a predominantly Shiite area in eastern Baghdad earlier Wednesday, killing one person and wounding six, police said.

The explosion occurred at 10 a.m. after the driver parked the car near a currency exchange office in the Amin district in New Baghdad neighborhood, then walked away.

"A seemingly normal person parked this car and told us that he would not be long," said the owner of the currency exchange who identified himself as Abu Talal. "When that person disappeared for more than 20 minutes, we tried to call the police but the car exploded as we were trying to do so."

Shop owners in Baghdad often insist that motorists get permission before parking their cars due to the frequent bombings that hit the capital, which is facing rising sectarian violence.

Police found the body of one person killed thrown into a nearby alley by the force of the blast, while six others were wounded. The blast also damaged several nearby shops.

Iraqi security forces also have been frequent targets of insurgent attacks as they are seen as collaborators with U.S.-led forces.

A suicide bomber driving an oil truck blew himself up after he was stopped at a checkpoint near an Iraqi army headquarters north of Baghdad on Wednesday, wounding 9 soldiers, an officer said.

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The attacker apparently planned to drive the truck into the compound in Muqdadiyah, but guards stopped him at the checkpoint about 100 yards away at about 9:15 a.m. He detonated his explosives belt as he got out of the vehicle, causing it to explode as well, army Col. Ibrahim Hussein said.

The blast came just over a month after a suicide bomber struck a police station in Muqdadiyah, 60 miles north of Baghdad, killing seven officers.

A parked car bomb also struck a police patrol in the northern city of Mosul at about 10:30 a.m., killing one policeman and wounding two others, Brig. Abdul Karim al-Jibouri said.

Elsewhere, six tortured bodies were found blindfolded and with their hands and legs bound in Fallujah, 40 miles west of Baghdad, hospital officials said.

The bloodshed Tuesday took place despite heightened security following a battle with messianic Shiites who authorities said planned a large assault on Ashoura ceremonies. With security so intense at the main venues, extremists chose targets in smaller cities where safety measures were less stringent.

A suicide bomber blew himself up among a crowd of worshippers entering a Shiite mosque in Mandali near the Iranian border, killing 26 people and wounding 47, according to police. At least 12 more died and 28 were wounded when a bomb exploded in a garbage can as Shiites were performing outdoor rituals in the largely Kurdish city of Khanaqin, police said.

In Baghdad, gunmen in two cars opened fire on a bus carrying pilgrims to the capital's most important Shiite shrine, killing seven and wounding seven, police said. Hours later, mortar shells rained down on two mostly Sunni neighborhoods, killing nine and wounding 30 in what police said appeared to be a reprisal attack.

Ashoura ceremonies mark the 7th-century death of Imam Hussein, grandson of the Prophet Mohammad, in a battle near Karbala that cemented the Sunni-Shiite schism. Worshippers beat themselves with chains, slice their heads with knives and pound their chests in expressions of grief over the death of Imam Hussein.

Security has been tight at the commemorations since a string of bombings and suicide attacks killed at least 181 people at Shiite shrines in Baghdad and Karbala in 2004. Last year's Ashoura commemorations were largely peaceful, but suicide bombers killed 55 Shiites in 2005.

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