Iranians are voting to elect a new president, with all but one of the four candidates regarded as hardliners, APA reports citing BBC.
The winner will replace incumbent Hassan Rouhani, a relative moderate who has served the maximum two terms.
Dissidents and some reformists have called for a boycott, saying the barring of several contenders has removed any genuine competition.
The elections come at a time of widespread discontent among Iranians over economic hardships.
Supreme Leader Ayatollah Ali Khamenei cast his vote early on Friday morning in Tehran and encouraged people to go the polls.
"Each vote counts ... come and vote and choose your president," he said. "This is important for the future of your country,"
However, there is widespread apathy among voters, after three years of crippling sanctions reinstated by the US when it abandoned a nuclear deal between world powers and Iran.
The elections coincide with the latest round of talks in Vienna aimed at reviving the accord, which saw Iran agree to limit its nuclear programme in return for sanctions relief.
Almost 600 hopefuls, including 40 women, registered for the election.
But in the end only seven men were approved last month by the 12 jurists and theologians on the hardline Guardian Council, an unelected body that has the ultimate decision with regard to candidates' qualifications.