Baghdad ? A string of bombings targeted Shiite worshippers in the Baghdad area during Friday prayers, killing at least 29 people in an apparently coordinated attack against followers of an anti-U.S. cleric who were blamed for some of Iraq’s worst sectarian violence.

The blasts shattered a recent calm and underscored warnings that suspected Sunni insurgents would step up efforts to stoke sectarian violence as the Americans draw down their forces. Despite the violence, July remained one of the calmest months for Iraqis and the least deadly for American forces.

The largest blast was a car bombing near the al-Shoroufi mosque that killed at least 24 people and wounded nearly 30 in the northern neighborhood of Shaab, a former stronghold of the militia led by Muqtada al-Sadr, whose forces were accused of being behind sectarian bloodshed and were routed last year in a U.S.-backed government offensive.