"Today is a blessed day for the Iranians in which people in fact decides about the fate of their country and contribute to the destiny of their homeland", asserted the incumbent president who is hopeful to win the election for the second term.
Rouhani, considered a moderate, was a key architect of the 2015 nuclear deal with the USA, the European Union and other partners.
Rouhani, who has framed the vote as a choice between greater civil liberties and "extremism", faces stiff competition from hardline cleric Ebrahim Raisi, 56, who has positioned himself as a defender of the poor and called for a much tougher line with the West.
If no-one wins more than 50% of votes cast, a run-off will be held next week.
Rouhani, a longtime establishment insider and former nuclear negotiator, won the presidency in 2013, bolstered by the support of many Iranians yearning for less repression.
"Everyone should vote in this important election".
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Rouhani voted about an hour later. Ballot counting will start at midnight and final results are expected within 24 hours of polls closing, the semi-official Fars news agency said. "I will vote for Raisi". In a hypothetical second round between the two front-runners, 91% of respondents said their minds were made up, and 60% of those said they preferred Mr Rouhani. Raisi has even been discussed as a possible successor to him, though Khamenei has stopped short of endorsing anyone. Reformist voters highlight Mr Raisi's part in some of Iran's darkest times: in the Eighties he was a judge on the "death commissions" that sent thousands of political prisoners to the gallows and firing squads.
Rouhani, a cleric, says his moderate administration needs to continue its work to implement the nuclear deal.
He is believed to have the backing of the powerful Revolutionary Guards security force, as well as the tacit support of Khamenei, whose powers outrank those of the elected president but who normally steers clear of day-to-day politics.
Unemployment remains high - although it fell during Rouhani's first term - and growth is middling.
"Rouhani has skillfully...permitted Iranian youth to repeat what happened in 2013 on a larger scale - namely projecting their wishes onto a candidate who is not a reformist but (still) embraces reformist rhetoric", said Behnam Ben Taleblu, senior Iran analyst at the Foundation for Defense of Democracies (FDD) in Washington.
Despite the removal of nuclear-related sanctions in 2016, lingering unilateral United States sanctions that target Iran's record on human rights and terrorism have kept many foreign companies wary of putting stakes in the Iranian market.
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The Haryana Board of School Education (HBSE) is all set to announce the results of Class X on Saturday. In humanities, Smile from Fatehabad and Kusum of Sonipat scored 483 marks each to be the toppers.
Hard-liners remain suspicious of America, decades after the 1953 U.S. -engineered coup that toppled Iran's prime minister and the 1979 U.S. Embassy takeover and hostage crisis in Tehran. Both deny the other's accusations.
Iran's Supreme Leader Grand Ayatollah Ali Khamenei was among the first to cast his ballot and urged others to do the same.
All of this must be taken into account with one additional factor at play: The Islamic Republic after Khamenei. He could pose the biggest challenge to Rouhani, especially if he can unify hard-liners.
For the election, Rouhani has pinned his hopes on people who are undecided or do not usually vote.
There is little chance Raisi will ease social restrictions or release opposition leaders held under house arrest since the 2009 protest movement, known to conservatives as "the sedition". Although the supreme leader did not single out any candidate, it was easy to read it as aimed at Rouhani. Iran's Guardian Council, a 12-member panel half selected by the supreme leader and half nominated by the judiciary and approved by parliament, vetted the candidates and narrowed the field to six, including Rouhani.
Supporters of the two leading candidates honked, blared music and held pictures of the hopefuls out of vehicle 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. "What matters most is the turnout, not the result", he said.
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On Monday morning before the BBC interview he was accosted by reporters outside his home, but he cycled away without a reply. Some patients have had their appointments cancelled or have been unable to schedule a new appointment.
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