Baghdad ? 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 also were killed and one was wounded, the officer said, speaking on condition of anonymity because he feared retribution.

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.

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.