At least 717 people taking part in the Hajj pilgrimage have been killed in a stampede near the Islamic holy city of Mecca, officials in Saudi Arabia say.
Another 863 people were injured in the incident at Mina, which occurred as two million pilgrims were taking part in the Hajj’s last major rite.
It is the deadliest incident to occur during the pilgrimage in 25 years.
King Salman has ordered an urgent review of this year’s Hajj plans “to improve the level of organisation”.
The supreme leader of Iran, which lost at least 95 of its citizens in the crush, has criticised Saudi Arabia’s preparedness.
It is the second disaster to strike Mecca in two weeks, after a crane collapsed at the Grand Mosque, killing 109 people.
Accounts from BBC staff in Mina
During the Hajj, pilgrims travel to Mina, a large valley about 5km (3 miles) from Mecca, to throw seven stones at pillars called Jamarat, which represent the devil.
The pillars stand where Satan is believed to have tempted the Prophet Abraham.
People were going towards the direction of throwing the stones while others were coming from the opposite direction. Then it became chaotic and suddenly people started going down.
There were people from Nigeria, Niger, Chad and Senegal among other nationalities. People were just climbing on top of others in order to move to a safer place and that’s how some people died.
People were chanting Allah’s name while others were crying, including children and infants. People fell on the ground seeking help but there was no-one to give them a helping hand. Everybody seemed to be on their own.
It affected some members of our group. I lost my aunt as a result of the stampede and at the moment, two women from our entourage -a mother and her daughter-are still missing.
Maj Gen Mansour al-Turki, a spokesman for the Saudi interior ministry, said the crush occurred when two large groups of pilgrims converged from different directions on to one street.
Photographs showed the bodies of dozens of pilgrims on the ground, some piled high.They were all dressed in the simple white garments worn during the Hajj.