The blast tore through a procession of pilgrims on one of the holiest days for Shiites.
Witnesses said a suicide bomber was disguised as a volunteer handing out juice and food to pilgrims near the southern town of Zubair.
But an Iraqi military intelligence officer said they were killed by a roadside bomb.
Nearly 140 people were also wounded in the attack. It's the latest in a series of attacks aimed at Iraq's majority Shiites which have escalated following the withdrawal of U.S. troops.
