Iran's Ayatollah Ali Khamenei has blamed mismanagement by Saudi Arabian authorities for a deadly stampede that left more than 700 pilgrims dead, including at least 90 Iranians.
The country's supreme leader declared three days of mourning to mark the tragedy in comments published by the state news agency IRNA.
"The government of Saudi Arabia must accept the huge responsibility for this catastrophe," Khameini said of the incident, which also left at least 863 people injured.
Earlier, the deputy foreign minister, Hossein Amir Abdollahian said Saudi's envoy to Tehran would be summoned to the foreign ministry.
The head of Iran's Hajj organisation, Said Ohadi, said that, for "unknown reasons," two paths had been closed off near the site of a symbolic stoning of the devil ritual where the stampede occurred.
"This caused this tragic incident," he said on state television, according to the Associated Press news agency.
The names of all Iranians killed in the stampede were read out in a sombre live broadcast in Tehran by a spokesman for the Hajj organisation.
Ohadi said the path closures had left only three routes to the area where the stoning ceremony was held in Mina, about 5km from Mecca.
'Lack of serious attention'
"Today's incident shows mismanagement and lack of serious attention to the safety of pilgrims," said Ohadi.
"There is no other explanation. The Saudi officials should be held accountable."
Abdollahian also accused Saudi officials of "tactlessness" over the lack of safety measures at the Hajj.
"We can in no way be indifferent to this irresponsible behaviour of Saudi Arabia. This will be dealt with through diplomatic channels," he said on state television.
Saudi Health Minister Khaled al-Falih has blamed undisciplined pilgrims for the tragedy, saying it could have been avoided if they had "followed instructions."
Iran has set up a special headquarters at the accident site to support Iranian pilgrims.