Bangladesh, May 25 -- The sacred Hajj pilgrimage officially begins today as millions of Muslims from around the world gather in the holy city of Makkah, Saudi Arabia, to perform one of the most important religious obligations in Islam.

Pilgrims were seen offering prayers at the Grand Mosque on Sunday ahead of the formal commencement of the annual pilgrimage.

The first three days of Hajj are regarded as the principal phase of the pilgrimage, as pilgrims travel between Mina, Arafat and Muzdalifah, taking part in prayers, sermons and symbolic rituals associated with Islamic history and tradition.

Hajj is one of the five pillars of Islam and is obligatory once in a lifetime for Muslims who are physically and financially capable of underta...