Saudi King Salman bin Abdulaziz has announced an investigation into a stampede and crush at the annual hajj in Mecca, in which at least 717 people died. Iran, which lost 90 citizens, says the blame lies with Riyadh.
King Salman announced an investigation, saying he had given instructions for a review of "all existing plans and arrangements ... to improve the level of organization and management of the movement" of pilgrims at the hajj.
"This sad accident, into which we have ordered authorities to launch an investigation and provide us with results as soon as possible, will not be allowed to degrade the great services we extend to the guests of God to perform their rituals," the monarch said.
The stampede broke out in Mina, as pilgrims headed for the symbolic stoning of the devil ritual on the third day of the hajj.
Saudi officials initially put the blame on "undisciplined pilgrims" who had "not followed instructions." The authorities said the safety measures at Mina, where Hajjis (pilgrims) throw pebbles at a depiction of the devil as part of Islamic tradition, were foolproof.
'Huge responsibility for catastrophe'
However, the supreme leader of Iran said Saudi Arabia was responsible for the stampede, claiming that improper measures and mismanagement of the hajj were to blame.
Ayatollah Ali Khameni announced three days of mourning, and demanded that the cause of the accident - in which at least 90 Iranian pilgrims died - "should not be overlooked."
"The government of Saudi Arabia must accept the huge responsibility for this catastrophe," state news agency IRNA quoted Khameni as saying.
Tehran envoy called in
Deputy Foreign Minister Hossein Amir Abdollahian said earlier that Saudi's envoy to Tehran would be summoned to the foreign ministry over the stampede.
The hajj, which attracted 2 million people from more than 180 countries this year, always provides asignificant logistical challenge for Saudi Arabia.
Thursday's incident is the deadliest since 1990, when 1,426 people died in a stampede in a pedestrian tunnel leading from Mecca towards Mina. The last time there were such significant casualties at the Hajj was in 2006, also in Mina, when a stampede during the stoning of the Devil killed at least 346.
Only a week ago, a construction crane collapsed in Mecca's Grand Mosque and killed 108.