The pilgrims have arrived in the city on foot, by cars, buses and many other means from Iraq, Iran, Saudi Arabia, Lebanon, Bahrain, Pakistan and countries as far as Nigeria, PRESS TV reports.

The religious ceremony marks the 40th day after the martyrdom anniversary of the grandson of Prophet Mohammad (PBUH), Imam Hussain (PBUH).

According to Iraqi authorities, some 17 million people have arrived on Friday in the holy city and three million more are expected for today.

The Arba’een ceremony is one of the largest religious gatherings in the world.

Iraqi forces have tightened security to protect the pilgrims against terrorist attacks. The Iraqi government has also adopted measures for an easier evacuation of pilgrims from Karbala.

Imam Hussain (PBUH) and his 72 companions were martyred in the battle of Karbala on the day of Ashura in 680 CE, after refusing to pledge allegiance to the tyrant ruler of his time.