BAGHDAD (AP) – Roadside bombs killed the top Shiite official in a volatile area south of Baghdad and an anti-al-Qaida Sunni sheik to the north Thursday as internal power struggles within both Islamic sects threaten to complicate U.S. efforts to stabilize the country.

Car bombs, meanwhile, struck Iraqi civilians in Baghdad and the northern city of Tal Afar, with at least 31 people killed or found dead nationwide, according to police reports.

Abbas Hassan Hamza, a political moderate and the top official in the Iskandariyah district, was killed by a bomb that struck his convoy while he was going to work, a police officer said. Four of his bodyguards were killed and one was wounded, the officer said, speaking on condition of anonymity.

Hamza had defected two years ago to Prime Minister Nouri al-Maliki’s Dawa Party from the largest Shiite party, now known as the Supreme Islamic Iraqi Council.

Suspicion for the killing fell on Shiite extremists jockeying for power ahead of expected provincial elections.

Iskandariyah has a volatile mixed population that is about 60 percent Shiite and 40 percent Sunni. The Mahdi Army militia, loyal to radical Shiite cleric Muqtada al-Sadr, is active in the area, some 30 miles south of Baghdad. The Sadrists boycotted the previous provincial elections in January 2005, ceding most local leadership posts to Supreme Islamic Iraqi Council and other rival groups.

Rising internal violence threatens to plunge the southern Shiite heartland into political turmoil.

The tensions pose a dilemma for the U.S. military, which must decide whether to intervene in what essentially is a civil conflict even as critics step up calls to start withdrawing U.S. troops.

Meanwhile, Sheik Muawiya Naji Jbara, the Sunni head of the Salahuddin Tribal Awakening Council, died from head injuries he suffered after a roadside bomb exploded as his convoy traveled near Samarra, 60 miles north of Baghdad, said his brother, Marwan Jbara. He said two guards also were wounded.

The blast occurred as the prominent sheik was traveling to an area southwest of Samarra to support the anti-al-Qaida fighters there, a day after 16 members of the council were wounded during clashes with gunmen, according to his brother.

Nobody claimed responsibility for the attack, but al-Qaida-linked Sunni insurgents have been fighting back against initiatives promoted by the American military to turn Sunni sheiks against the terror network.

U.S. and Iraqi troops meanwhile detained a lawmaker from Iraq’s biggest Sunni bloc after he allegedly attended a meeting of suspected al-Qaida in Iraq fighters.

Naif Jassim Mohammed was taken into custody Wednesday during a funeral for one of his neighbors in Shurqat, about 140 miles north of Baghdad, according to Salim Abdullah, a spokesman for the Iraq Accordance Front, an alliance of three parties that have 44 of parliament’s 275 seats. He said he didn’t know why Mohammed was arrested.

The U.S. military said American and Iraqi troops acting on a tip seized a member of parliament Saturday. It did not identify the man other than to say he was a “suspected criminal leader.”

He was being held for questioning “after being found at a suspected al-Qaida in Iraq meeting,” according to a statement.

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Associated Press writers Bushra Juhi and Sinan Salaheddin contributed to this report.