Warning: Video report contains images some may find distressing
The Saudi authorities have been criticised after a crush of two large columns of people during the Hajj pilgrimage - the latest in a line of disasters around Mecca.
Millions of pounds have been spent on expanding the shrine area in Mecca, but, as ITV News International Affairs Editor Rageh Omaar reports, the precautions put in place were not able to prevent the latest in a line of catastrophes.
Iran's supreme leader has called on the Saudi government to accept responsibility for a crush that killed more than 700 worshippers outside Mecca.
Ayatollah Ali Khamenei alleged that "mismanagement and improper actions have caused this catastrophe".
Iran's state news agency IRNA has reported that at least 95 Iranians were among the dead following the disaster.
Saudi King Salman has ordered a review of the country's plans for the annual Hajj pilgrimage following today's devastating crush near the Muslim holy city of Mecca.
In a speech broadcast live on television, he added that he had asked for a swift investigation into what he described as a painful incident.
Foreign Secretary Philip Hammond has expressed sadness at the "enormous loss of life in Mecca" after hundreds were killed in a crush during the Hajj pilgrimage.
It is currently unclear whether any Britons were among those killed and injured, and Hammond said Foreign Office staff were "in close contact with the Saudi authorities and tour operators, and are checking hospitals and other locations to urgently gather information about British nationals who may require assistance."
"We are also deploying further staff from the region to bolster our response," he said.
I was saddened to hear of the enormous loss of life in Mecca. My thoughts are with families and victims at this difficult time. Such a significant tragedy will affect Muslims across the world who take part in the Hajj pilgrimage.
Anyone concerned about British nationals attending the pilgrimage is advised to telephone the embassy in Riyadh or tweet the FCO Twitter account.
The grim aftermath of the crowd crush near Mecca has been revealed as amateur videos and photos were posted on social media.
Lifeless bodies were seen on the ground dressed in the simple terry cloth garments worn during the Hajj pilgrimage.
Victims' arms were draped over the heads and shoulders of others who perished, while rescue teams worked to free those still alive from the mass of bodies.
Other pictures showed people sitting in wheelchairs and being treated.
The head of the Council of British Hajjis has told ITV News it will prove "very hard" to locate 20,000 British pilgrims in the initial aftermath of the Hajj stampede, despite some tour operators calling in to confirm their group's safety.
Chief executive Rashid Mogradia defended Saudi security measures for the world's largest gathering of people.
He said anyone unable to contact British loved ones attending the Hajj can contact the council via its website at http://cbhuk.org/
A British Muslim pilgrim attending the Hajj has told ITV News he is "horrified" at the hundreds of deaths near Mecca.
Mohammed Adree Sharif said he was "shocked" at the reports as the event "seemed to be well organised" as he joined two million other pilgrims in the stoning ritual.
Doctors rush those hurt in the Hajj crush to the emergency hospital in Mina.
Staff at Emergency Hospital in Mina rush to rescue injured from the Hajj stampede —State TV http://t.co/Iew57HPyul
The death toll from the crush in Saudi Arabia has risen to 717 and at least 805 others are injured, according to the Saudi Civil Defence.
Anyone concerned about British nationals attending the Hajj pilgrimage is advised to telephone the embassy in Riyadh or tweet the FCO travel advice account.
The Council of British Hajjis has said anyone unable to contact British loved ones attending the Hajj can contact the council via its website at http://cbhuk.org/