The U.S. military said it killed four suspected terrorists and four civilians Wednesday in a raid in Baqouba, while Iraqi forces announced they had arrested a leader of a militant group believed responsible for numerous attacks on coalition forces. Scattered violence killed 13 people while 15 more bodies were found.

In the southern city of Basra, British and Iraqi troops launched an ambitious security operation aimed at rooting out corrupt police, pacifying the city and helping residents rebuild, the British military said.

The U.S. command also announced the deaths of a Marine and a U.S. soldier, both of whom were killed in action Monday western Anbar province of Iraq.

The violence came as U.S. military spokesman Maj. Gen. William B. Caldwell said attacks against civilians and coalition forces have spiked in Baghdad since the Muslim holy month of Ramadan began this weekend.

"We are seeing an increase in attacks, as anticipated. The terrorists and illegal armed groups are punching back in an effort to discredit the government of Iraq and more specifically the Baghdad security plan," Caldwell said.

CountryWatch: Iraq

Thirteen people were killed in scattered violence while the mutilated corpses of another fifteen apparent death squad victims were discovered.

The corpses of nine people were pulled out of the Tigris river and turned in to the morgue in Kut, 100 miles southeast of Baghdad. They had been blindfolded, had their hands and legs tied, and showed signs of torture, Mahmoun Ajeel al-Rubaie said.

The body of a civilian kidnapped the night before was also turned in to the morgue after being found in an industrial area of the city, al-Rubaie said.

Later, five beheaded corpses were brought to the morgue, found on the banks of the Tigris in Suwayrah, 25 miles south of Baghdad.

In Baghdad, five people were killed and six others injured when a parked car bomb blew up near a fuel station in a southwest district of the city, police said.

Earlier, Captain Jameel Abbas of the capital's Major Crimes Bureau was killed when a bomb hidden in his car detonated at 8:30 a.m. (0430 GMT), police Lt. Bilal Ali Majeed said. The blast on the city center's Rasheed Street also wounded one passer by, Majeed said.

There are currently 45,000 Iraqi and 15,000 U.S. coalition forces operating in Baghdad, he said.

Operation Together Forward, a security drive to clear the capital neighborhood by neighborhood was launched this summer after U.S. generals warned escalating sectarian violence was leading toward civil war. Sweeps have been started or completed in about half the neighborhoods of the capital so far.

In Baqouba, 35 miles northeast of Baghdad, American soldiers came under fire when approaching the home of a suspect linked to the leaders of Al Qaeda in Iraq, the U.S. command said in a statement.

U.S. troops killed two terrorist suspects, then called in air strikes "due to the heavy volume of enemy fire from the target building," the military said. After the attack, they found the bodies of two more terror suspects and four women inside the building.

Three people were wounded, including two suspected terrorists who were later detained.

The troops also found weapons and a global positioning system, the military said.

A family member said all eight people killed were relatives and disputed that they had any links to a terrorist organization. "The Americans killed my relatives who had no guilt or relation with any group," Saleh Ali said in a telephone interview with The Associated Press.

In Baghdad, meanwhile, the Iraqi General Command of the Armed Forces said another leader of the militant 1920 Revolution Brigades had been arrested Tuesday night in the village of al-Jazira.

The operation follows the arrest of another leader of the group and seven aides early Saturday in the same area, about 60 miles north of Baghdad.

Authorities have not released the insurgents' names, citing security concerns.

The Sunni militant group, a mixture of Iraqi nationalists and Islamic extremists, is believed to be responsible for numerous attacks against U.S. forces and a series of kidnappings. It was one of seven Sunni Arab insurgent groups the government said in June had contacted authorities to declare their readiness to join in efforts at national reconciliation.

Some 2,300 Iraqi army troops and 1,000 British soldiers launched the security drive in Basra dubbed "Operation Sinbad," with another 2,000 British troops conducting operations in the surrounding area, said British forces spokesman Maj. Charlie Burbridge.

The operations, which aims to pacify the city while helping rebuild the infrastructure, was expected to take months, he said. A key component is a crackdown on police corruption, and a special team will be going station-by-station to weed out those involved in it, he said.

"We're gradually inching our way forward. Ultimately our aim here is to take Basra to a place where it can be turned over to Iraqi control," he said in a telephone interview from southern Iraq.

Iraqi troops were providing security for Iraqi engineers conducting "low level immediate impact projects" like repairs to two schools and the building of a footbridge, Burbridge said.

"At this stage, it's the beginning of the operation," he said, adding that longer term projects were to follow.

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In June, Prime Minister Nouri al-Maliki declared a state of emergency in Basra following a rise in violence among mostly Shiite groups competing for power in the predominantly Shiite city. Basra is located about 340 miles southeast of the capital near the Iranian border.

Since January 2005, the city has fallen under the influence of Shiite militias, which have infiltrated the police and local government institutions there.