Iranians began voting on Friday in a run-off election to replace the late president Ebrahim Raisi, who was killed in a helicopter crash in May.

Voters face a choice between the hardline former nuclear negotiator Saeed Jalili and Masoud Pezeshkian, a heart surgeon and long-time parliament member who has allied himself with moderates and reformists within Iran’s Shiite theocracy.

An initial round of voting on June 28 saw no candidate get more than 50% of the vote, forcing the run-off. It also saw the lowest turnout for an Iranian election, leaving turnout on Friday a major question.

There have been calls for a boycott, including from imprisoned Nobel Peace Prize laureate Narges Mohammadi, although potential voters in Iran appear to have made the decision not to participate last week on their own as there is no widely accepted opposition movement operating within or outside of the country.

As has been the case since the 1979 Islamic Revolution, women and those calling for radical change have been barred from the ballot while the vote itself will have no oversight from internationally recognised monitors.

The voting comes as wider tensions have gripped the Middle East over the Israel-Hamas war in the Gaza Strip.

In April, Iran launched its first direct attack on Israel over the war in Gaza, while militia groups that Tehran arms in the region — such as the Lebanese Hezbollah and Yemen’s Houthi rebels — are engaged in the fighting and have escalated their attacks.

Meanwhile, Iran continues to enrich uranium at near weapons-grade levels and maintains a stockpile large enough to build — should it choose to do so — several nuclear weapons.

Its 2015 nuclear deal with world powers, reached by officials now backing Pezeshkian, collapsed in 2018 after then-president Donald Trump unilaterally withdrew America from the accord. In the time since, hardliners have taken control of all levers of power within Iran’s government.

While Iran’s 85-year-old Supreme Leader Ayatollah Ali Khamenei has the final say on all matters of state, presidents can bend the country’s policies toward confrontation or negotiation with the West.

Interior minister Ahmad Vahidi, who is in charge of overseeing the election, announced all the polls had opened at 8am local time. Typically, Ayatollah Khamenei casts one of the election’s first votes.

More than 61 million Iranians over the age of 18 are eligible to vote with about 18 million of them between 18 to 30.

Friday’s election marks only Iran’s second presidential run-off since 1979. The first came in 2005, when hardliner Mahmoud Ahmadinejad beat former president Akbar Hashemi Rafsanjani. Under Mr Ahmadinejad, Iran faced international sanctions over its advancing nuclear programme, as well as the 2009 Green Movement protests and the crackdown that smashed them.

Mr Pezeshkian’s supporters have been warning Mr Jalili will bring a “Taliban”-style government into Tehran, while Mr Jalili has criticised his opponent for running a campaign of fear-mongering.

Mr Raisi died in the May 19 helicopter crash that also killed the country’s foreign minister and others.