Millions of mourners in Karbala to mark Arba’een

Millions of pilgrims from across the world are in Iraq's holy city of Karbala to mark 40 days since the martyrdom anniversary of Imam Hussein, the grandson of Prophet Muhammad.

Large groups of black-clad mourners, many of whom have reached Karbala after trekking at least 76 kilometers from Najaf, are observing Arba'een, known as the largest annual religious gathering on earth.

Arba'een, meaning the fortieth in Arabic, is observed 40 days after Ashura, the tenth day of the lunar calendar month of Muharram, when Imam Hussein, the third Shia Imam, was martyred at the hands of the tyrant of the time, Yazid I, back in the seventh century.

Imam Hussein is a highly-venerated figure not only among Shia Mulims but also Sunnis, Christians and the people of other faiths.

Iraq has tightened security in and around Karbala, which is home to Imam Hussein's holy shrine, stationing tens of thousands of security personnel near the perimeters of the sanctuary as well as on all roads leading to the city.

Tents have been erected along the routes, with volunteers distributing food and drinks to the pilgrims arriving from different Iraqi cities and other countries, including Iran, Azerbaijan, Yemen, Turkey, Oman, Bahrain, India, Pakistan and Lebanon.

Every year, millions of pilgrims reach Karbala for Arba'een from across Iraq and abroad, especially neighboring Iran, which marked the occasion this year on Thursday.

According to the spokesman for Iran's Arba'een ceremony committee, Shahriar Heidari, so far 2.3 million Iranians have traveled to Iraq to mark Arba'een this year, with more expected to arrive there on Friday.

Drone footage captured on the eve of Arba'een showed millions of people gathering in the holy city.