At least 31 people were killed and 100 injured in a stampede during the Ashura ceremony in the holy city of Karbala, 100 km south of Baghdad.
Medical and security sources said the death toll was not definitive and that it was likely to rise due to the intensity of visitors.
Hundreds of thousands of Shiites in Iraq today commemorated the death of Hussein bin Ali bin Abi Talib, may Allah be pleased with them, amid tight security.
The ceremony began in the early hours of this morning, especially in the city of Karbala (118 km south of Baghdad) at the shrine of Imam Hussein, in a tradition used by Shiite Iraqis to revive it.
The Iraqi government declared Tuesday an official holiday and deployed tens of thousands of troops, police, security services and the Popular Mobilization Forces to provide protection for condolences.
The defense and interior ministers, army chiefs and all military and security leaders and the Popular Mobilization supervised the implementation of insurance plans.