Iranians head to polls to elect new president

He faces stiff competition from hardliner Ebrahim Raisi, 56, who has positioned himself as a defender of the poor and called for a much tougher line with the West.

Supreme leader Ayatollah Ali Khamenei cast his ballot just minutes after polls opened at 8:00 am (0330 GMT).

"The destiny of the country is in the hand of Iranians," he told reporters as he voted in Tehran. 

After casting his ballot, Rouhani said whomever the voters elect as president should receive all of the nation's support.

"Any candidate who is elected should be helped to accomplish this heavy responsibility," Rouhani said.

"Anyone who is elected must be helped from tomorrow with unity, happiness and joy."

Long lines had already formed at polling stations in the capital.

Iranian authorities say they believe the vote will exceed a 70 percent turnout.

Rouhani has pushed the boundaries over the past fortnight, criticising the continued arrest of reformist leaders and activists, and calling on security agencies not to interfere in the vote.

Raisi says he will stick by the 2015 nuclear deal with world powers, that saw curbs to Iran's atomic programme in exchange for sanctions relief, but he points to the continued economic slump as proof that Rouhani's diplomatic efforts have failed.

	Supreme leader Ayatollah Ali Khamenei casts his ballot [Getty]

A voter from Iran’s holy city of Qom told AP he has voted for Raisi.

"Rouhani has turned our foreign policies into a mess and damaged our religion," said Sedigheh Davoodabadi, a 59-year-old woman said. "Rouhani gave everything to the US outright" in the nuclear deal.

Iranians overseas also will vote in over 300 locations, including 55 in the US, where more than one million Iranians live.

The race has heated emotions and pushed public discourse in Iran into areas typically untouched in the tightly controlled state media.

That includes Rouhani openly criticising hard-liners and Iran's powerful Revolutionary Guard, a paramilitary force now involved in the war in Syria and the fight against Islamic State militants in neighbouring Iraq.

Rouhani also found himself surrounded by angry coal miners who beat and threw rocks at his armoured SUV during a visit to a northern mine struck by an explosion earlier this month that killed at least 42 people.

But authorities worry about tempers rising too high, especially after the 2009 disputed re-election of former hard-line President Mahmoud Ahmadinejad that saw unrest, mass arrests and killings.

Authorities barred Ahmadinejad from running in Friday's election, and Khamenei days ago warned anyone fomenting unrest "will definitely be slapped in the face."

That hasn't stopped those at Rouhani rallies from shouting for the house-arrested leaders of the 2009's Green Movement. Opposition websites have said Green Movement leaders Mir Hossein Mousavi and Mahdi Karroubi both have endorsed Rouhani against Raisi. Rouhani promised in his 2013 campaign to free the men, but that pledge so far remains unfulfilled.

Mohammad Khatami, another reformist who served as Iran's president from 1997 to 2005, also has endorsed Rouhani.

Supporters of the two leading candidates honked, blared music and held pictures of the hopefuls out of car windows on the traffic-clogged and heavily policed streets of Tehran late into the night Thursday, ignoring a ban on campaigning in the final 24 hours before the vote.

Voting is scheduled to run until 18:00, though Iran routinely extends voting for several hours in elections.

Agencies contributed to this report