A homicide truck bomber struck a Sunni tribal leader's house near the Syrian border on Wednesday, killing at least five people in the latest attack by suspected Sunni extremists on provincial officials and tribal figures.

Bombers also struck Iraqi civilians as a total of at least 24 people were killed or found dead in areas to the north and south of the capital.

Nobody claimed responsibility for the attacks, but they bore the hallmarks of Al Qaeda in Iraq, which has warned that it planned a new campaign of violence during the Islamic holy month of Ramadan.

A U.S. soldier also was killed during a small-arms attack in eastern Baghdad on Tuesday, the military said in a statement issued Wednesday.

The U.S. military acknowledged attacks had increased in recent days, including attacks on police and tribal leaders presumably by Sunni extremists.

"We have seen an upturn in levels of violence in the last few days and so we are continuing our efforts to suppress it and keep the pressure on extremist networks," Maj. Gen. Kevin Bergner told reporters. "We will continue to keep that focus because we know that this is a specific period of time ... that the insurgents will try to increase the levels of violence."

Bergner also said Iraqi and U.S. forces had raided an Iraqi military academy in eastern Baghdad and detained employees accused of involvement in the kidnapping and killing of the institution's former commander as well as the kidnapping of the current commander, who was subsequently freed. He said the suspects also were accused of using their positions and access to sell weapons.

Defense Ministry spokesman Maj. Gen. Mohammed al-Askari said those detained faced charges of murder, kidnapping and administrative corruption.

"These suspects were criminal gangs, not militiamen, working for their own interests by using their posts in the Defense Ministry," he said.

The raid highlighted the overwhelming challenges in the U.S. strategy of preparing Iraqi forces to take over their own security despite endemic corruption and infiltration by Shiite militias.

Bergner acknowledged the problems but expressed confidence in the Iraqis, stressing the operation against the military academy in Rustamiyah was led by the Defense Ministry and showed it was committed to "policing its own ranks."

"This is very much a work in progress and it's most important that the government of Iraq and their ministries step up to those challenges and hold their people accountable," he said at a news conference in Baghdad.

The first blast occurred about 10:30 a.m. near the house of Sheik Kanaan Iqhaimar, the Sunni chieftain of the Mawali tribe, in a village some 55 miles west of Sinjar, according to the town's mayor.

Mayor Dukheel al-Sinjari said the sheik's son worked for the Iraqi government as a contractor. Insurgents frequently have targeted Iraqi government employees and other officials they accuse of collaborating with U.S.-led efforts in the country.

The attack also occurred in the same area where quadruple bombings struck Yazidi communities, a small Kurdish-speaking religious sect in northern Iraq.

Al-Sinjari said five people were killed and nine wounded, including the sheik. He said the casualty toll could rise because more bodies were believed to be under the rubble.

A parked car bomb also exploded near a group of black market gasoline vendors in a town elsewhere in northern Iraq, killing at least five people and wounding seven, police said. Another bomb struck wounded victims as they were being taken to the hospital.

The blast from the car bomb was intensified when the barrels of gasoline being sold exploded in the center of Shurqat, 140 miles north of Baghdad, according to the police officials, who spoke on condition of anonymity because they weren't authorized to release the information.

Homcide car bombers struck two separate areas in the northern city of Mosul. At least three people were killed and 30 wounded in a blast at a building construction site. At about the same time, Iraqi soldiers opened fire on a suspected bomber targeting their patrol elsewhere in the city. The bomber managed to detonate his explosives before he was killed, leaving three civilians dead and one soldier wounded, police Brig. Gen. Saeed Ahmed al-Jubouri said.

A series of other bombings have struck police officers and Shiite and Sunni leaders who have joined forces with U.S.-led forces against Al Qaeda in Iraq in recent days.

On Tuesday, a suicide car bomber attacked a police headquarters in the southern city of Basra, killing at least three policemen, wounding 20 people. Local authorities blamed Al Qaeda, saying the terror network was trying to take advantage of the deteriorating security situation in the city.

An al-Qaida front group — the Islamic State of Iraq — also claimed responsibility for a suicide bombing near the entrance of a mosque where a U.S.-promoted reconciliation meeting was being held late Monday in Baqouba, the Diyala provincial capital 35 miles northeast of Baghdad. The police chief and two other senior officers were among the 24 people the military said were killed.

Diyala provincial leaders pledged to push ahead with efforts to bring Shiites and Sunnis together a day after the devastating suicide attack at the sectarian unity meeting in the provincial capital, Baqouba. At least 37 people were wounded, U.S. and Iraqi officials said.