Here is some background on a nation whose influence stretches from Iraq to Syria, Lebanon and Yemen, but which is grappling with a severe economic crisis.
Successor to the ancient Persian Empire ruled by monarchs called shahs, military strongman Reza Shah Pahlavi took the throne in 1925 after years of upheaval.
He was forced to abdicate in 1941 in favour of his son Mohammad Reza after Britain and the Soviet Union invaded.
Prime Minister Mohammad Mossadegh, who had nationalised the British-controlled oil industry, is ousted in a 1953 coup orchestrated by London and Washington.
Shiite cleric Ayatollah Ruhollah Khomeini, the leader of opposition to the shah’s modernising reforms, is deported in 1964.
Anti-government demonstrations and strikes erupt in January 1978. In the face of the growing protests, the shah leaves the country in January 1979.
Khomeini, who had led the uprising from exile, makes a triumphant return in February from France.
An Islamic republic is proclaimed on April 1, with Khomeini its first supreme leader.
Iran’s constitution gives the final say on all issues of state to the supreme leader, whose authority trumps that of the elected president.
The role is taken by Ayatollah Ali Khamenei after Khomeini’s death in 1989.
An elected council of vetted clerics, the Assembly of Experts, oversees the work of the supreme leader and has the authority to dismiss him.
Next in line is the president, who names the government and is elected for four years by universal suffrage.
Moderate cleric Hassan Rouhani, now 72, became president in 2013 and won a second term in 2017.
He replaced populist Mahmoud Ahmadinejad whose re-election in 2009 had sparked massive protests and a government crackdown.
Parliament’s powers are limited. Legislation is vetted by the Guardian Council made up of 12 clerics and jurists, who have the authority to reject measures they deem contrary to Islam or the constitution.
The Revolutionary Guards, armed forces wedded to the ideology of the state, are particularly influential.
Iran is holding more than a dozen Western citizens, most of them dual nationals, in prison or under house arrest in what activists say is a brazen act of hostage-taking to extract concessions.
Shiite-majority Iran rivals Sunni kingpin Saudi Arabia for influence in the Middle East, the two taking opposing sides in multiple regional conflicts.
Tehran has been the main regional backer of Syrian President Bashar al-Assad against Riyadh-backed Sunni rebels since civil war broke out in 2011.
In Yemen, Iran supports Shiite rebels who still control most of the north, including the capital Sanaa, despite more than six years of Saudi-led military intervention.
In Lebanon, Iran-backed Shiite militant group Hezbollah plays a pivotal role in political life, while its fighters are heavily involved in neighbouring Syria in support of Assad‘s government.
In 2015, Iran struck a landmark agreement with major powers after 12 years of on-off negotiations to accept limits on its nuclear programme in exchange for an easing of crippling sanctions.
But then US president Donald Trump withdrew from the hard-won accord in 2018 and reimposed sanctions.
The other parties have vowed to keep the accord alive, and talks have been held in Vienna to rescue it.
Iran is a founding member of the Organization of the Petroleum Exporting Countries and sits on the world’s fourth-largest oil reserves and second-largest gas reserves.
But it suffers from chronic unemployment and high inflation, and Washington’s reimposition of sanctions sent its currency tumbling.