The holy city of Karbala has been host to a religious event termed by observers as the one of the largest in the country. Millions of pilgrims have already poured into the city and still many are heading there for Arbaeen.

Arbaeen marks the 40th day after the martyrdom of Imam Hossein, the Prophet Muhammad's grandson and the third Imam in Shia Islam. Imam Hussain was martyred in the battle of Karbala in the year 61 Hijri calendar (680 in the Gregorian calendar).

Millions of Shia Muslims from both inside and outside Iraq travelled to Karbala on foot, to take part in the mourning of Arbaeen.

Tight security measures were put in place with a large number of security personnel deployed in Iraq 's holy sites in preparation for the occasion. The pilgrims praised the efforts of the security forces.

Karbala which is home to the shrine of Imam Hussein lies 110 kilometers south of the Iraqi capital Baghdad. Since Wednesday at least 46 people have been killed in four attacks on worshippers.

The Iraqi government has deployed Thousands of policemen and soldiers in and around Karbala to protect the pilgrims