Voters flocked to the polls to weigh in on the country's faltering economy and aggressive foreign policy.
Street demonstrations quieted ahead of intensely anticipated presidential vote on Friday.
Supporters of challenger Mir Hossein Mousavi clash with riot police and Hizbullah vigilantes.
Tens of thousands have rallied in favor of Ahmadinejad challenger Mousavi ahead of June 12 election.
Mahmoud Ahmadinejad faces a surge from the more moderate challenger Mir Hossein Mousavi, as more educated urban voters tire of his polarizing politics.
Days before June 12 vote, Mir Hossein Mousavi gets 'savoir's' welcome in a former presidential stronghold
Presidential campaign politics intrude on the anniversary of Islamic republic's founder.
President Mahmoud Ahmadinejad faced off against one of his three opponents, Mir Hossein Mousavi, Wednesday night in the second of six debates leading up to June 12 elections.