Millions of pilgrims gathered in Iraq's holy city of Karbala amid tight security Wednesday to mark Arbaeen, the annual commemoration of the end of the 40-day mourning period over the killing of Imam Hussein, the Prophet Mohammad's grandson, in A.D. 680 .

Iraqi state-run media said Wednesday that more than 22 million pilgrims have visited Karbala, setting a record for the annual pilgrimage.

Iraqi authorities said last year's Arbaeen drew 17 million pilgrims.

A suicide bomber targeted pilgrims in Baghdad Monday, killing nine people and wounding another 21, according to Iraqi security officials.

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