Iranians are voting to elect a new president in an electoral process highly controlled by the government.
News agencies in Iran are reporting Friday that officials have extended the voting hours because of a high turnout. Some 55 million people are eligible to vote.
Citizens can choose among six remaining candidates who were approved by a panel of ruling clerics. Most are considered hardliners who support the government structure and are loyal to the country's supreme leader.
Iran's Supreme Leader Ayatollah Ali Khamenei cast his vote in Tehran Friday. Afterward, he rejected U.S. criticism of the election, saying Iran would be a "loser" if it waited to see what Americans accepted.
Iran sealed most of its borders, rounded up dissidents and detained some journalists. Most foreign news organizations say their attempts to get visas to cover the election were unheeded by the government.
The winner will be the successor to two-term President Mahmoud Ahmadinejad, who is constitutionally barred from a third consecutive term.
Iran's supreme leader has been calling for Iranians to show up to vote in large numbers.
Heading into the campaign, many analysts viewed Iran's chief nuclear negotiator, Saeed Jalili, as the likely favorite. But moderate candidate and former nuclear negotiator Hassan Rowhani has been gaining prominence in recent days.
One candidate seen as reformist, Mohammad Reza Aref, dropped out this week and then announced his support for Rowhani. Another candidate, Gholam Ali Haddad Adel, dropped out of contention Monday saying he wanted to boost the chances of his fellow conservatives.
The election winner will be faced with an economy struggling with high unemployment and inflation, crippled by international sanctions imposed over Iran's disputed nuclear program.
While some candidates have voiced support for improved ties with the international community, major policy decisions rest with the supreme leader.
To win, a candidate must get 50 percent of the vote. If no one succeeds after the initial vote, a runoff election will be scheduled a week later.