Iranian election officials say President Mahmoud Ahmadinejad has taken a commanding lead over reformist rival Mir Hossein Mousavi in his bid for re-election.
Results show that with nearly 70 percent of the votes counted, Mr. Ahmadinejad won 66 percent to 31 percent for Mr. Mousavi, a former Iranian prime minister.
Iran's state news agency has declared Mr. Ahmadinejad the winner, but Mr. Mousavi also claimed victory late Friday at a news conference in Tehran. He did not give details to support his claim. He also said there were problems with the voting due to a shortage of ballots in some areas.
Iran's election Friday appeared to be a tight race between Mr. Ahmadinejad, the conservative incumbent, and Mr. Mousavi, the top reformist candidate.
Iranians lined up to vote in massive numbers, and officials extended voting hours to accommodate long lines.
Election commission chief Kamran Daneshjou said turnout was "unprecedented." Officials predicted a turnout of 70 percent or more of Iran's 46 million eligible voters.
Reformist cleric Mehdi Karroubi and conservative former Revolutionary Guards commander Mohsen Rezaei also competed in the poll, in which Iran's economy, nuclear program and foreign relations were said to play a key role.
Mr. Mousavi urged election officials to comply with the law Friday, after some of his representatives were reported to have been blocked from entering polling stations to monitor the voting.
Mr. Ahmadinejad's rivals have accused him of badly mismanaging the economy and tarnishing Iran's image, further isolating the country from the West.
If no candidate wins an outright majority, the two leading candidates will face each other in a run-off vote on June 19.
Some information for this report was provided by AFP, AP and Reuters.