A series of bomb attacks in Iraq Monday struck Shi'ite pilgrims performing the annual Ashura rituals, killing at least 28 people and wounding more than 80 others.

Police said that in the first and deadliest attack in the central Iraqi city of Hilla, a car bomb tore through a procession. At least 16 people — mostly women and children — were killed and 45 others wounded.

A second attack in Hilla, involving a roadside bomb, killed at least two people and wounded three others.

Three more attacks against Shi'ite pilgrims in the capital Baghdad claimed the lives of at least 10 people and wounded another 38, police said.

Ashura, a Shi'ite day of mourning, commemorates the seventh-century killing of Imam Hussein, a grandson of the Prophet Muhammad, during a battle with rival Muslims.

The blasts took place at a time of heightened concern about Baghdad's ability to handle security after the U.S. military completes its withdrawal from Iraq by the end of 2011. The pullout will end a military presence in the country that began with the 2003 U.S.-led invasion that toppled Iraq's dictator Saddam Hussein.

Violence in Iraq has declined from the peak of sectarian fighting in 2006 and 2007, but insurgent attacks remain common.