KERBALA, Iraq (Reuters) - Millions of Shi’ites Muslims gathered at shrines and mosques in Kerbala and other parts of Iraq on Thursday to mark the climax of the annual ritual of Ashura with expressions of suffering.

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Huge crowds came from all over the world to commemorate the slaying of Imam Hussein, grandson of the Prophet Mohammed.

Most Sunni Muslims also mourn Hussein’s death, but less fervently, and Ashura is a reminder of Sunni-Shi’ite rifts dating from disputes over the Prophet Mohammad’s succession.

In the past, suicide bombers staged attacks on the mass gathering hoping to trigger sectarian tensions.

Those days are gone. Iraqi worshippers are able to immerse themselves in their faith, setting aside other problems that impact daily lives, including poor government services, unemployment and corruption.

Ashura is the 10th day of the lunar month of Muharram when according to Islamic tradition Imam Hussein was killed in battle in 680.

It is observed in Iraq and in other countries with sizeable Shi’ite communities, including Afghanistan, Azerbaijan, Bahrain, Iran, Lebanon, Pakistan, Saudi Arabia and Syria.

On the first day of Muharram, the army of Caliph Yazid laid siege to Hussein and followers in the desert near Kerbala. Hussein was killed in battle 10 days later after he had refused to pledge allegiance to Yazid.

Hussein was decapitated and his head was taken to Damascus, the seat of the Ummayad dynasty to which Yazid belonged.

Self-flagellation is a big part of the ritual.

On Thursday, crowds of pilgrims brandished swords. One man gashed the head of a teenager with a knife. Blood dripped down their heads to white smocks. A pilgrim banged a drum.

“Blood is but a simple thing we offer to Hussein. All we offer Hussein is actually nothing,” said pilgrim Haider Sabah.

“Even if we give our lives for him it is not enough. We are ready to offer all we have, our lives, our children and our families for Hussein to have his intercession in doomsday.”