About three million Muslims, including thousands from the Middle East, India, Pakistan, the U.S., Russia and Europe, are expected to attend the Bishwa Ijtema, which starts on Friday and culminates Sunday in a mass prayer along the River Turaq in Tongi, just north of Dhaka.

Bangladeshi authorities stepped up security, with thousands of troops deployed to the area.

Volunteers set up tents for Muslim worshippers, and troops installed seven temporary bridges over the river.

Security forces are manning entry points from towers and are using metal detectors and sniffer dogs to search for weapons. More than 50 security cameras have also been installed.

Last year, more than 2.5 million Muslims participated in the event, held annually since 1966.

The Bishwa Ijtema is usually organized by the World Tablig Council, which preaches the teachings of Islam and Prophet Muhammad (PBUH).

The gathering is mainly aimed at reviving the tenets of Islam and promoting peace and harmony. Participants usually discuss the holy Qur'an, and hear sermons by Muslim scholars from around the world.

The event also focuses on prayers and meditation, and doesn't allow political discussions, organizers said.

About 87 percent of Bangladesh's 144 million people are Muslim.