Iraqi police said a mortar attack killed one person and wounded four others near Karbala on December 12 as record numbers of Shi'ite pilgrims gathered in the shrine city for one of the largest annual religious gatherings in the world.
Iraqi Defense Minister Khaled al-Obeidi said on December 11 that more than 17 million pilgrims had come to Karbala for the Arbaeen commemoration.
Arbaeen, which falls on December 13 this year, marks the end of a 40-day mourning period for the anniversary of the death of Imam Hussein, the Prophet Muhammad's grandson.
Millions of pilgrims have come from neighboring Iran, a predominantly Shi'ite country. Iraq has reportedly waived the $40 visa fee for Iranian nationals.
The festival has been marred by deadly attacks in previous years.
This year's commemorations come with portions of Iraq under the control of militants from Islamic State, a Sunni extremist group that considers Shi'ites to be heretics and has made targeting the community one of its main objectives.