Hundreds of thousands of Muslim pilgrims are converging on the Iraqi holy city of Karbala to commemorate Arbaeen, Press TV reported.
The event marks the culmination of a 40-day mourning period after the anniversary of the martyrdom of Imam Hussein, Prophet Muhammad's grandson and the third Shia Imam.
Imam Hussein and his 72 faithful companions were martyred in an unequal battle with the enemies of Islam in Karbala over 1300 years ago.
Around 30,000 police forces have been deployed in and around the city to try to bolster security for the event.
This comes as at least 12 people were killed and more than 30 others injured in two bomb explosions that ripped through a Karbala neighborhood on Monday.
The car bombs went off at a parking lot, destroying several nearby vehicles and buildings in the al-Ibrahimiyah area in eastern Karbala, police sources said.
Iraqi officials also reported six separate attacks in the Iraqi capital, Baghdad, on Sunday.
Violence and sporadic high-profile bomb attacks continue in Iraqi cities, threatening the lives of citizens.