The Iranian constitution outlines specific procedures to follow in the event of a president's sudden absence.
Here is what happens after President Ebrahim Raisi's death in a helicopter crash on Sunday:
Who assumes President Raisi's powers?
Article 131 of the constitution states that in case of the president's death, dismissal, resignation, extended absence or illness, or when a new president has not been elected, the first deputy assumes powers with the approval of Iran's supreme leader Ayatollah Ali Khamenei.
Mohammad Mokhber is the First Vice President.
When will elections be held in Iran?
A council, comprising the Speaker of Parliament, the head of the judicial branch and the president's first deputy, must arrange an election within 50 days.
If the president's first deputy cannot perform duties due to death or other reasons, or if there is no first deputy, the supreme leader appoints a replacement.
What happens during this period?
Article 132 of the constitution states that during the period when the first deputy or another appointed person assumes presidential powers, ministers cannot be dismissed.
A vote of no-confidence cannot be passed against ministers, and constitutional amendments and national referendums cannot be initiated.
Mr Khamenei said on Sunday that “there will be no disruption in the work of the country” during this period, according to state-run media.
What are the Iranian president’s primary duties?
The president is the head of the Council of Ministers. He “supervises the work of the ministers and takes all necessary measures to coordinate the decisions of the government,” according to the constitution.
He determines the agenda and policies of the government and implements the laws.
“In the case of discrepancies or interference in the constitutional duties of the government agencies, the decision of the Council of Ministers at the request of the President shall be binding provided it does not call for an interpretation of or modification in the laws,” says the constitution's text.
How is President Raisi regarded?
President Ebrahim Raisi's absence is important because he served as the second-in-command in Iran's ruling structure after the supreme leader.
Many Iranians expected him to be considered as a successor to Mr Khamenei, as Mr Raisi had a religious, political, judicial and administrative background, and he created the image of an official fighting corruption.
He was also a member of the Assembly of Experts, which includes members of the clergy and politicians charged with choosing the supreme leader.