Vowing to contest the results, Ahmadinejad's main rival and a reformist candidate Hossein Mousavi alleged massive rigging in the polls.
The votes counted so far in the presidential poll show that Mahmoud Ahmadinejad has been re-elected, the BBC said, quoting Iran's poll panel.
The report says Ahmadinejad has 65% of the vote with 80% counted and has claimed victory in an election that drew a large turnout.