A series of explosions rocked Baghdad and cities throughout Iraq Thursday. More than 30 people were killed and about 100 wounded in 12 separate bombings.

Officials said extremists launched attacks in the Iraqi capital and in the cities of Kirkuk, Samarra, Baqouba, Dibis, and Taji.

Mortars were fired into the northern cities of Beiji and Tikrit, Saddam Hussein's hometown, but no injuries were reported in either city.

About half the attacks targeted security forces and government officials. Most occurred in Shiite neighborhoods, where residents suffered the greatest casualties.

No one has claimed responsibility for Thursday's bombings, but officials say the attacks fit the pattern of al Qaeda.

The violence is causing concern that insurgents are trying to weaken the Shiite-led government and stir sectarian strife.

Overall, attacks have dropped sharply nationwide since Iraq threatened to dissolve into civil war five years ago.

Violence recently waned since the run-up to the Arab League summit, held in Baghdad at the end of March. But sporadic bombings and deadly shootings across the country are still common.

Iraq's fragile coalition government appeared poised to break down for months, following the U.S. troop withdrawal in late December.