Up to 25 people were killed and 75 wounded in a car bomb explosion in the city of Diwaniyah, the capital of Muthanna province in southern Iraq on Tuesday, a local police source said, dpa reported.
The bombers blew themselves up simultaneously during processions in the shrine city, 118 kilometres south of the capital Baghdad.
The attack came despite heightened security to protect thousand of pilgrims who head to Karbala for the commemoration on Thursday of the birth of the last Shiite Imam.
Most Shiite Muslims believe that Imam al-Mahdi, who was born in the ninth century, will return to establish justice on earth.
Some 40,000 personnel are involved in an operation to secure the event, including 2,000 policewomen and women volunteers who search female pilgrims.
In June, blasts targeting Shiite pilgrims in Baghdad killed 100 people