Polls opened Friday for the tightest presidential election in Iran's history, with relative moderate and frontrunner Akbar Hashemi Rafsanjani facing a tough challenge from both reformist and hardline contenders.
The Islamic republic's supreme leader Ayatollah Ali Khamenei, among the first to cast his ballot, urged Iranians to support his regime by voting en masse a day after the United States savaged its standards of democracy.
"No matter who we vote for - it's a vote for the system," the top cleric said.
The election, expected to go into a nail-biting second round, marks the end of eight years of frustrated efforts by President Mohammad Khatami to reform the 26-year-old theocracy.
Iran's interior minister said that turnout in presidential election “is relatively good and the "very close" competition means the polls are likely to go into a second round.”
"My assessment is that the election will be a two-phase one, because the competition is very close," said Abdolvahed Moussavi Lari, whose ministry is in charge of organising the election.
"The participation, based on the information we have so far, is relatively good," he added, saying turnout appeared to be more than during parliamentary elections in February 2004 - when 50.5 percent of eligible voters cast their ballots.
Rafsanjani is hoping his image as a pragmatist with clout can lure voters who are tired of political deadlock.
"Some opinion polls say there will be someone elected in the first round. I hope that will be the case," the 70-year-old ayatollah told reporters as he voted in leafy north Tehran.
"I voted for myself," quipped the charismatic cleric, whose main rivals are leftist reformer Mostafa Moin and hardliner Mohammad Baqer Qalibaf.
Rafsanjani, who was Iran's president from 1989 to 1997, has presented himself as a man opposed to "extremists", open to restoring ties with Washington and committed to easing international tensions over the country's nuclear programme.
Voting ends at 7:00 pm (1430 GMT), but can be extended until midnight. First results are expected Saturday.
US President George W. Bush has charged that the election in the Middle East's most populous nation, already lumped into his "axis of evil", "ignores the basic requirements of democracy."
"Power is in the hands of an unelected few," Bush said. "Iran's rulers denied more than a thousand people who put themselves forward as candidates, including popular reformers and women."
Khamenei responded by accusing Iran's foreign "enemies" of encouraging voters to snub the election so they can argue "that Islam could not create a true democratic regime."
Khamenei's comments emphasise the concern over turnout, amid widespread apathy and calls for a boycott from students and prominent liberals including Nobel Peace Prize Winner Shirin Ebadi.
The election, which a month ago looked like a one-horse race, looks set to be the tightest in Iran's history.
None of the seven candidates is expected to win more than 50 percent of votes, and Rafsanjani may be forced into an unprecedented second round run-off - on June 24 or July 1 - with either Moin or former police chief and Revolutionary Guards veteran Qalibaf.
Even though candidates have been pre-screened and the real power will remain in the hands of the deeply-conservative supreme leader, the seven contenders are offering very different visions.
Unlike Khamenei, Rafsanjani favours economic liberalisation and closer ties with the West - even if he once branded Bush a "bird-brained dinosaur."
The silver-haired regime veteran, who served as the middle man in the "Irangate" weapons for hostages deal in the 1980s, has been campaigning as a savvy deal-maker but remains the target of corruption allegations.
It also remains to be seen if he still inspires a country where 70 percent of the population is under 30 and where 15-year-olds have the vote.
Former higher education minister Moin - initially disqualified from standing - has promised to free political prisoners, challenge the powers of unelected hardliners and name a cabinet dominated by dissident leftists.
He is hoping for an upset similar to Khatami's spectacular 1997 landslide win, even though the wave of popular euphoria that brought Khatami to power has long dissipated.
The main hardline challenger is Qalibaf, who has reinvented himself as a trendy technocrat who promises a bread-and-butter focus in a country rich in oil and gas but dogged by high unemployment.
His critics have cast him as a Khamenei man, and have reignited memories of his support for a crackdown on pro-democracy student demonstrators in 1999.
Pre-election projections by one polling institute said Rafsanjani was due to score 24-28 percent, Qalibaf 14-16 percent, and Moin 12-15 percent - but the margin for error is extremely wide.
Security is also tight, amid fears of a repeat of the bomb attacks that killed up to 10 people nearly a week ago.