Iranian state TV said the country's Supreme Leader Ayatollah Ali Khamenei has died.
State TV gave no cause for the 86-year-old's death, with the announcement following joint US-Israeli strikes on the country.
It comes after US President Donald Trump claimed Khamenei had died in the attacks on Saturday morning and urged the Iranian people to seize "the single greatest chance ... to take back their country".
The UK Government has not yet commented on reports of the Ayatollah's death, but shadow foreign secretary Dame Priti Patel said: "No-one should shed any tears for the death of Khamenei."
Saturday's attack prompted retaliation from Iran, with strikes reported in several Gulf countries including the United Arab Emirates, Qatar, Bahrain and Saudi Arabia.
Hundreds of thousands of British nationals are believed to be present in the Gulf, and those in Bahrain, Israel, Palestine, Qatar and the UAE have been urged to register their presence with the Foreign Office.
The death of Supreme Leader Ayatollah Ali Khamenei after almost 37 years in power raises paramount questions about Iran's future. The contours of a complex succession process began to take shape the morning after Khamenei's assassination.
Here is what to know:
Temporary leadership council
As outlined in its constitution, Iran on Sunday formed a council to assume leadership duties and govern the country.
The council is made up of Iran's sitting president, the head of the country's judiciary and a member of the Guardian Council chosen by Iran's Expediency Council, which advises the supreme leader and settles disputes with parliament.
Iran's reformist president, Masoud Pezeshkian, and hard-line judiciary chief Gholamhossein Mohseni Ejei, are its members who will step in and "temporarily assume all the duties of leadership."
Panel of clerics
Though the leadership council will govern in the interim, an 88-member panel called the Assembly of Experts "must, as soon as possible" pick a new supreme leader under Iranian law.
The panel consists entirely of Shiite clerics who are popularly elected every eight years and whose candidacies are approved by the Guardian Council, Iran's constitutional watchdog.
That body is known for disqualifying candidates in various elections in Iran and the Assembly of Experts is no different. The Guardian Council barred former Iranian President Hassan Rouhani, a relative moderate whose administration struck the 2015 nuclear deal with world powers, from election for the Assembly of Experts in March 2024.
Khamenei's son
Clerical deliberations about succession and machinations over it take place far from the public eye, making it hard to gauge who may be a top contender.
Previously, it was thought that Khamenei's protege, hard-line President Ebrahim Raisi, may try to take the mantle. However, he was killed in a May 2024 helicopter crash.
That has left one of Khamenei's sons, Mojtaba, a 56-year-old Shiite cleric, as a potential candidate, though he has never held government office.
But a father-to-son transfer in the case of a supreme leader could spark anger, not only among Iranians already critical of clerical rule, but also among supporters of the system. Some may see it as un-Islamic and in line with creating a new, religious dynasty after the 1979 collapse of the U.S.-backed Shah Mohammad Reza Pahlavi's government.
Rare transition
There has been only one other transfer of power in the office of supreme leader of Iran, the paramount decision-maker since the country's 1979 Islamic Revolution.
In 1989, Grand Ayatollah Ruhollah Khomeini died at age 86 after being the figurehead of the revolution and leading Iran through its eight-year war with Iraq. This transition now comes after Israel launched a 12-day war against Iran in June 2025 as well.
Vast powers
The supreme leader is at the heart of Iran's complex power-sharing Shiite theocracy and has final say over all matters of state.
He also serves as the commander-in-chief of the country's military and the powerful Revolutionary Guard, a paramilitary force that the United States designated a terrorist organization in 2019, and which Khamenei empowered during his rule.
The Guard, which has led the self-described "Axis of Resistance," a series of militant groups and allies across the Middle East meant to counter the U.S. and Israel, also has extensive wealth and holdings in Iran.
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