Muslim pilgrims cast their stones at a pillar symbolising the stoning of Satan during the annual haj pilgrimage in Mina, Saudi Arabia August 11, 2019. Muslims from around the world hurled pebbles at a giant wall in a symbolic stoning of the devil on Sunday, the start of the riskiest part of the annual haj pilgrimage in Saudi Arabia, where hundreds died in a crush four years ago. REUTERS/Umit Bektas

Muslim pilgrims walk to cast their stones at a pillar symbolising the stoning of Satan during the annual haj pilgrimage in Mina, Saudi Arabia August 11, 2019. The kingdom stakes its reputation on its guardianship of Islam's holiest sites, Mecca and Medina, and organising the world's largest annual Muslim gathering which retraces the route Prophet Mohammad took 14 centuries ago. REUTERS/Umit Bektas

Muslim pilgrims walk to cast their stones at a pillar symbolising the stoning of Satan during the annual haj pilgrimage in Mina, Saudi Arabia August 11, 2019. Tens of thousands of security forces and medics are deployed alongside modern technology including surveillance drones to maintain order. REUTERS/Umit Bektas

Muslim pilgrims cast their stones at a pillar symbolising the stoning of Satan during the annual haj pilgrimage in Mina, Saudi Arabia August 11, 2019. Nearly 2,5 million pilgrims, mostly from abroad, have arrived for the five-day ritual, a religious duty once in a lifetime for every able-bodied Muslim who can afford it. They are asked to follow carefully orchestrated schedules for each stage of haj, but with so many people, panic is a constant danger. REUTERSUmit Bektas

A Muslim pilgrim counts her stones to cast at a pillar symbolising the stoning of Satan during the annual haj pilgrimage in Mina, Saudi Arabia August 11, 2019. Under close supervision and clad in white robes signifying a state of purity, the faithful converged on Jamarat to perform the stoning ritual from a three-storey bridge erected to ease congestion after stampedes in previous years. REUTERSUmit Bektas

Muslim pilgrims cast their stones at a pillar symbolising the stoning of Satan during the annual haj pilgrimage in Mina, Saudi Arabia August 11, 2019. They will return to the bridge over the next two days for more stoning before returning to Mecca to pray at the Grand Mosque at the end of haj. REUTERS/Umit Bektas