At least 717 pilgrims were killed on Thursday in a stampede outside the Muslim holy city of Mecca, Saudi authorities said, the worst disaster to strike the annual hajj pilgrimage in 25 years.

At least 805 others were injured in the crush at Mina, a few kilometers east of Mecca, caused by two large groups of pilgrims arriving together at a crossroads on their way to performing the "stoning the devil" ritual at Jamarat, Saudi civil defense said.

Thursday's disaster was the worst to befall the pilgrimage since July 1990, when 1,426 pilgrims were crushed to death in a tunnel near Mecca. Both stampedes occurred on Eid al-Adha (Feast of the Sacrifice), Islam's most important feast and the day of the stoning ritual.

"Work is underway to separate large groups of people and direct pilgrims to alternative routes," Saudi Civil Defense said.

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Safety during the hajj is a politically sensitive issue for the kingdom's ruling Al Saud dynasty, which presents itself internationally as the guardian of orthodox Islam and custodian of its holiest places in Mecca and Medina.

An Arab pilgrim who did not want to give his name said he had hoped to perform the stoning ritual later on Thursday afternoon but was now too frightened to risk doing so.

"I am very tired already, and after this, I can't go. I will wait for the night, and if it not resolved, I will see if maybe somebody else can do it on my behalf," he said.

Two weeks ago 110 people died in Mecca's Grand Mosque when a crane collapsed during a storm and toppled off the roof into the main courtyard, crushing pilgrims underneath.