Iraqi officials say a twin bombing has killed nine Shiites in a town south of Baghdad as they were marking a somber religious ritual.

A police officer says two bombs exploded simultaneously in Hafriyah, about 50 kilometers (32 miles) from the Iraqi capital, as a group of Shiites were observing the Ashoura. The annual ritual commemorates the 7th century death of Prophet Mohammed's grandson.

The officer says the bombing also wounded 31 people. A medical official confirmed the causality figures. Both spoke on condition of anonymity as they were not authorized to talk to media.

Ashoura attracts hundreds of thousands of Shiites. It's often targeted by Sunni extremists who consider Shiites to be heretics.

Violence has spiked in Iraq since April with more than 5,500 killed, according to U.N. figures.