Iranians are voting for a new president today in an election that analysts predict cleric Akbar Hashemi Rafsanjani will win in a tight poll.
Queues formed at some polling stations soon after they opened at 9am. Official results are expected on tomorrow.
Unelected Supreme Leader Ayatollah Ali Khamenei, among the first to vote, told Iranians they would be endorsing not just their chosen candidate, but their country's Islamic system.
“Whoever you vote for among those seven candidates, it's a vote for him, the Islamic republic and the constitution,” he said after using a special ballot box at his official residence.
Mr Rafsanjani has topped most opinion polls, often unreliable in the past, ahead of what is expected to be Iran's closest election since the 1979 Islamic revolution.
“I have promised people to continue reforms and I am sure I can deliver my promises,” he said after voting.
The moderate cleric, seeking to regain the office he held from 1989 to 1997, needs 50 per cent support to avoid an unprecedented run-off between the two top vote-getters.
His closest challengers are reformist former education minister Mostafa Moin (54), and conservative ex-police chief Mohammad Baqer Qalibaf (43), although conservative former Tehran mayor Mahmoud Ahmadinejad appears to have gained ground.
Thousands of people jammed streets to welcome Mr Ahmadinejad to the southern city of Isfahan on a recent campaign trip. The crowd's enthusiasm delayed his speech by hours, witnesses said.