KARBALA, Iraq (Reuters) -- Tens of thousands of Iraqi Shi'ite pilgrims, defying the threat of suicide attacks, have flocked to a shrine to mark Arbain, one of the most important events in the Shi'ite Muslim religious calendar.
Pilgrims crowded the Imam Hussein Mosque in Karbala, 80 kilometers south of Baghdad, some beating their chests or heads in ritual mourning for Hussein, the Prophet Muhammad's grandson, who died in battle in the seventh century.
Iraqi officials say millions of people have visited Karbala in the last week for the ritual, which culminates early on February 16 and marks the end of 40 days of mourning.
The annual event draws hundreds of thousands from Iraq's Shi'ite majority, who were unable to practice such rites freely under former leader Saddam Hussein, a Sunni Arab. Shi'a also come from neighboring Iran and as far away as Pakistan.
Some Sunni Islamist groups like Al-Qaeda view Shi'a as heretics. Arbain and other major Shi'ite rituals have been a target for devastating attacks since Saddam was ousted in the U.S.-led invasion of 2003.
Some 42 pilgrims making their way to Karbala were killed in a suicide bombing on February 13. An attempted suicide bombing was foiled on February 14 in the same area after police pounced on a would-be attacker.
Shi'ite pilgrims were undeterred by the threat of violence.
"I came from Al-Basrah to challenge the terrorism and explosions," Abd al-Khedher Auda Jabar told Reuters Television.
Karbala police chief Ali al-Ghurairi said 30,000 police were out in force aiming to deter further attacks.
Policewomen were searching female pilgrims, whose voluminous black robes can easily conceal vests packed with explosives. Friday's bomber was a woman.
The climax of the pilgrimage is marked by a visit to Hussein's gilded grave, where worshippers weep and pray.
Violence has dropped sharply in Iraq, but attacks still occur routinely.