VIDEO: Pilgrims Crowd Iraqi Shrine Despite Attack

Tens of thousands of Iraqi Shi'ite pilgrims, defying the threat of suicide attacks, crowded into a shrine on Sunday to mark Arbain, one of the most important events in the Shi'ite Muslim religious calendar.

Pilgrims poured into the Imam Hussein mosque in Kerbala, 80 km (50 miles) south of Baghdad, some beating their chests or heads in ritual mourning for Hussein, the Prophet Mohammad's grandson, who died in battle in the seventh century.

Iraqi officials say millions of people have visited Kerbala in the last week for the ritual, which culminates early on Monday 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 practise such rites freely under former leader Saddam Hussein, a Sunni Arab. Shi'ites also come from neighbouring Iran and as far away as Pakistan.

Some Sunni Islamist groups like al Qaeda view Shi'ites as heretics. Arbain and other major Shi'ite rituals have been a target for attacks since Saddam was ousted in the U.S.-led invasion of 2003.

On Friday, 42 pilgrims making their way to Kerbala were killed in a suicide bombing. An attempted suicide bombing was foiled on Saturday in the same area after police pounced on a would-be attacker.

Yet as men wearing traditional Arab headdress and women cloaked in black crowded into a colonnade leading to the shrine, many said they were undeterred by the threat of violence.

"I came from Basra to challenge the terrorism and explosions," Abdul Khedher Auda Jabar told Reuters.

Abbas Kadhum, 70, said he had made the annual three-day trek from his home in Nassiriya for the last 40 years. "I do this to show my loyalty to my sect and to challenge those who try to make us abandon our rituals," he said.

Kerbala police chief Ali al-Ghurairi said 30,000 police were out in force aiming to deter further attacks. But policing such a crowded and often chaotic scene is a challenge.

Pilgrims complained of long security lines and insufficient accommodation in Kerbala. Many have to sleep in mosques or in the streets.

"The number of visitors has increased hugely and it's not enough to pat people down," said policeman Nadhum Ismael, who said police needed modern electronic equipment to detect bombs.

Policewomen have been 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.

More in the VIDEO: Security tight for Kerbala festival