Bombs targeting Shiite Muslims in areas south of Baghdad on Thursday killed 16 people and wounded 20 others, security and medical officials said.
Police and a medical said a car bomb exploded under a bridge in the shrine city of Karbala, killing five people and wounding 13.
A police spokesman said that security forces closed off all roads leading to the old city, where Imam Hussein, one of the most revered figures in Shiite Islam, is buried, and were searching for a second car bomb. In the city of Hilla, two roadside bombs targeted a group of Shiite pilgrims, killing three people and wounding seven others, police and a doctor said.
Members of Iraq's Shiite majority are often targeted by Sunni insurgents in bomb attacks.
Millions of pilgrims flock to Karbala each year for Ashura commemorations marking Hussein's death in 680 AD, which peaked on November 25 this year.
Pilgrims also walk from across Iraq to Karbala during the 40-day mourning period that follows Ashura.