Thousands of Iranians gathered in several cities to mourn Supreme Leader Ali Khamenei following reports of his death in joint U.S. and Israeli strikes, according to state media and international news agencies.

The question of who will succeed Ali Khamenei as Iran’s Supreme Leader has become a major subject of international political attention.

Iran’s Constitution clearly outlines the procedure to be followed in the event of the death, resignation, or incapacity of the Supreme Leader. The framework is set out in Article 111, which governs the transfer of authority and the selection of a successor.

Iranian Parliament Speaker Mohammad Bagher Ghalibaf has called the leaders of the United States and Israel “filthy criminals” who will face “devastating blows” for their ongoing attacks on the Islamic Republic, Al Jazeera reported on Sunday.

The office of Iranian President Masoud Pezeshkian condemned the killing of Supreme Leader Ayatollah Ali Khamenei “as a great crime” and vowed to respond, according to a statement from his office, Al Jazeera reported.

The Islamic Revolutionary Guard Corps (IRGC) has announced that it is carrying out a sixth wave of attacks in retaliation for the US and Israeli bombardment of Iran, Al Jazeera reported citing Iranian state media.

The Islamic Revolutionary Guard Corps (IRGC) has reportedly issued a statement responding to the death of Iran’s Supreme Leader Ayatollah Ali Khamenei, saying “we have lost a great leader and we mourn him,” Al Jazeera reported citing Fars News Agency.

The Qatari Ministry of Interior has reportedly stated that 16 people have been wounded following the attacks, Al Jazeera reported, citing local authorities.