Saudi Arabia’s King Salman has ordered a safety review for the Hajj pilgrimage after at least 717 people died in a stampede near the holy city of Mecca.
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.
The king said there was a need “to improve the level of organisation and management of movement” of pilgrims. It is the second disaster to strike Mecca in two weeks, after a crane collapsed at the Grand Mosque, killing 109 people.
As part of 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.
Offering condolences to the relatives of the dead and injured, King Salman said: “We have instructed concerned authorities to review the operations plan and to raise the level of organisation and management to ensure that the guests of God perform their rituals in comfort and ease.”
Saudi Arabia’s Crown Prince Mohammed bin Nayyef, who chairs the Hajj committee, has begun an inquiry into the tragedy.
Interior ministry spokesman, Mansour Turki, said the reason for the unusual number of pilgrims at the site of the disaster was “not known yet”.
Earlier, Health Minister Khaled al-Falih said the crush occurred because many pilgrims moved “without respecting the timetables” established by authorities.
However, Iran has fiercely criticised Saudi Arabia’s handling of the pilgrimage.
Announcing three days of national mourning, Supreme Leader Ayatollah Ali Khamenei said: “The Saudi government should accept the responsibility of this sorrowful incident… Mismanagement and improper actions have caused this catastrophe.”
The accident occurred at 09:00 local time (06:00 GMT) on Thursday as pilgrims were walking towards the five-storey structure which surrounds the pillars, known as the Jamarat Bridge.
Maj Gen Mansour al-Turki, a spokesman for the Saudi interior ministry, said two large groups of pilgrims had converged from different directions on to one street.
“I saw someone trip over someone in a wheelchair and several people tripping over him,” Abdullah Lotfy, from Egypt, told the Associated Press. “People were climbing over one another just to breathe.”
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.
“Dead bodies stretch as far as my eyes can see,” said Bashir Sa’ad Abdullahi, the BBC’s Abuja editor, who is in Mina.
The UK Foreign Office said it was urgently seeking more information about whether British nationals were involved.
Pope Francis, who is visiting the US, expressed his “sentiments of closeness” with Muslims, during a prayer service at St Patrick’s Cathedral in New York.
The Saudi authorities have spent billions of dollars on improving transport and other infrastructure to try to prevent such incidents.
The Hajj is the fifth and final pillar of Islam. It is the journey that every able-bodied adult Muslim must undertake at least once in their lives if they can afford it.
The number of people attending Hajj rose from 57,000 in 1921 to a high of 3.2m three years ago, according to the Saudi Central Department of Statistics and Information.
That figure dropped to just over two million last year.