With 20 percent of votes in, incumbent president leads with 69 percent :
TEHRAN, Iran (CNN) -- President Mahmoud Ahmadinejad was leading in early results from Iran's presidential election Friday, the election chief said.
With polls closed and about 20 percent of ballots counted, Election Commission Chief Kamran Daneshjoo said Ahmadinejad was ahead with just over 69 percent of the vote.
Daneshjoo said Ahmadinejad's chief rival, reformist candidate Mir Hossain Moussavi, had 28 percent.
Both candidates, however, were claiming victory.
Moussavi's campaign caught fire in recent days, triggering massive street rallies in Tehran. A large voter turnout Friday had been expected to boost his chances of winning the presidency.
Iranian voters crowded the steps of one polling place in Tehran, some waiting more than three hours underneath the hot sun to cast their ballots. Some were lining up even before the polls opened at 8 a.m.
Daneshjoo said the turnout was "unprecedented." State-run Press TV reported that as many as 32 million of Iran's 46 million eligible voters had cast a ballot Friday. iReport.com: Human chain for election in Iran
Voting was supposed to end after 10 hours, but because of the massive turnout, officials initially said polling stations would remain open until everyone in line had a chance to cast their ballot. However, doors were being closed with people still waiting outside.
Candidate profiles
Moussavi is the main challenger among three candidates vying to replace Ahmadinejad. The other candidates are former parliament speaker and reformist Mehdi Karrubi and Mohsen Rezaie, the former head of Iran's Revolutionary Guards.
Ahmadinejad still has staunch support in Iran's rural areas, but has been blamed for much of Iran's economic turmoil over the last four years. If he loses, it would be the first time a sitting Iranian president has not won re-election to a second term in office.
Text messaging was not working in Iran on Friday, something that Moussavi had been using to rally his supporters because of the candidate's lack of access to the mainstream media. But it is unlikely to have a significant impact on Moussavi's chances of winning, because voter turnout was so high.
If no single candidate reaches a simple majority -- 50 percent plus 1 vote -- a runoff election will be held on Friday, June 19.
There have been few reports of violence surrounding the election. However, several gunmen attacked Moussavi's election office in northern Tehran on Friday, an official with Moussavi's campaign told CNN's Shirzad Bozorgmehr. The attackers stormed into the office, hurled tear gas canisters and smashed several computers before the staff overpowered them and held them until police arrived, according to the official, Mohsen Amin Zadeh.
A few people were slightly injured in the attack. Police did not arrest the men and then threatened to close the election office, Zadeh said.
Fawaz Gerges, an academic and an author who studies the region, said Friday's vote is really "a referendum on Ahmadinejad," who has been in office since 2005.
"The unemployment rate is 30 percent ... the largest in the Third World, inflation is [in the] double digits in Iran," Gerges told CNN's "American Morning."
"We focus in the United States a great deal on his inflammatory rhetoric on the Holocaust, on nuclear weapons. We tend to forget that Ahmadinejad has basically done a great deal of damage to the Iranian economy, on social policy."
While Moussavi's campaign has energized key segments of Iranian voters, particularly women, Gerges noted that "Iranians have surprised us many times."
Moussavi's supporters crowded the streets of Tehran this week, wearing the candidate's trademark color green. His campaign has also energized Iran's youth, many of whom did not take part in the 2005 election. Yasmin, a 21-year-old university student, said she cast her ballot on Friday for Moussavi. CNN's Christiane Amanpour reports emotions on the street »
"I've never even been interested in the politics of my country until today. It was my first time voting, and I am so excited about it," she said. "We are all yearning for change, and I believe Moussavi will bring much more freedom to Iran and our lives. That is why I cast my ballot for him. There is so much anticipation in the air."
Moussavi's supporters hope he follows in the footsteps of Mohammed Khatami, a reformist candidate who overwhelmingly won the presidency in 1997, raising hopes that the reformist movement would bring religious and democratic freedoms to the Islamic republic. But the real power in Iran rests in the hands of Supreme Leader Ayatollah Ali Khamenei.
By the time Khatami left office in 2005, he was unable to make major changes because of the opposition of hard-line elements in Iran's clerical establishment.
"The elected president is not the commander in chief, he does not make decisions of war and peace," Gerges said. "The major decision maker [in Iran] is the unelected supreme leader, that is Ali Khamenei, along with a National Security Council."
But Gerges noted that the "the style of the president" and his "posture" have a great deal of influence on Iran's relations with other countries, particularly the United States.
No matter who wins Friday's vote, analysts say it is unlikely any of the candidates would change Iran's position on its nuclear program, which the Islamic republic says is for civilian purposes but the United States and other Western powers believe may be a cover for a weapons program.
Iranian-American analyst and scholar Reza Aslan said that while Moussavi is "a little bit more of a moderate when it comes to the nuclear issue ... all four candidates agree with Iran's right to develop nuclear."
Aslan said all four candidates also "recognize it's time to open up to America and to the international community, because there's no other option with regard to the economy." Watch CNN review the unprecedented online presence of candidates »
"But I think with Moussavi you have someone that I think would be more palatable for a Barack Obama to sit down next to," he told CNN's "American Morning."
The U.S. president has indicated his willingness to open dialogue with Iran -- something his predecessor was unwilling to do. But talks with the incumbent Iranian president are more likely to trigger criticism because of Ahmadinejad's controversial statements, including his repeated denial of the Holocaust and his comments about wiping Israel off the map.
Aslan predicted that Moussavi will emerge victorious after Friday's vote because of his ability to energize key segments of Iran's population.
"He's finally got the young people in Iran to care about politics again," Aslan said. "They really dropped out four years ago and they're back in full force now."
