The event kicked off at 8:00am local time (6:30am GMT).
Presidential election is also being held in 102 countries, IRNA reported.
For the presidential competition, the candidates are incumbent President Hassan Rouhani, the Custodian of Imam Reza (AS) Holy shrine Ebrahim Raeisi and former minister of Culture and Islamic Guidance Mostafa Aqa Mirsalim and former Minister of Physical Education Mostafa Hashemi Taba.
Polling stations are open from 8am until 6 p.m. local time (3:30am to 1:30pm GMT) although authorities have announced that the country's 63,500 polling stations could extend their voting time if necessary.
Over 56 million Iranians are eligible to vote in Iran's 12th presidential elections, according to the Election Headquarters of the Interior Ministry.
Out of the total eligible voters over 1.3 million are those who vote for the first time.
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