Long lines of people formed in front of polling stations across much of Iran Friday, as voters headed out to cast their ballots to choose between four candidates for president. A strong turnout, according to some analysts, could work against incumbent Mahmoud Ahmedinejad.

Iranian government TV urged voters to go to the polls, and it broadcast video of long lines of men and women standing outside polling stations across the country. Officials extended voting hours repeatedly.

Old women in wheelchairs, paralyzed war-veterans and religious leaders wearing turbans were shown waiting in line before casting their ballots.

Iran's Supreme Leader Ayatollah Ali Khamenei was welcomed by a crowd inside a polling station as he cast his ballot in front of a gaggle of photographers.

The Ayatollah delivered a pep-talk to the audience, after he voted, complaining that certain parties were trying to disrupt the elections and cause trouble.

He says that people will be hurt and damage will be done to the voting process if there is tension, so he urges everyone to prevent tensions and conflict. He also urges everyone to show patience and behave with dignity to fend off those with evil designs for the country.

Interior Minister Sadeq Mahsuli told journalists that election turnout was "unprecedented" and that he expected around 70 percent of the population to vote.

Election commission chief Kamran Daneshjou indicated that 35,000 polling stations across the country were being monitored directly by his office "online" and noted that voting will be extended by two hours because of the heavy turnout.

Iran's Press TV reported that many polling stations had run out of paper ballots during the course of the day, but that they were resupplied by the Interior Ministry.

Reformist candidate Mir Hossein Mousavi voted at a polling station south of Tehran, alongside his wife, who predicted that her husband "will win in the first round of voting, provided there is no vote-rigging."

Mousavi later complained to a local news agency that some of his representatives were denied access to certain polling stations, preventing them from monitoring the vote.

All three opponents of incumbent President Mahmoud Ahmedinejad, including Mousavi, Mehdi Karroubi, and Mohsen Rezaei have called on Supreme Leader Ayatollah Ali Khamenei to prevent any tampering with the vote.

Karroubi, a reformist former parliament speaker, told reporters that he was overjoyed by the heavy turnout as well as by the interest of the international press:

He says that he was told by foreign journalists that the election turnout is extraordinary and that this surprised them. It's great that these journalists are covering the election, he adds, and it indicates what a passionate and enthusiastic election we are having.

One Iranian voter, who gave his name as Mahdi Shahbaz, explained why he thought it was important to vote in this year's election:

He argues that elections are a wonderful thing for the Iranian people, and notes that many have not voted since the Iranian Revolution in 1979. But now, he says, they have come to realize how important elections are.

Forty-six-point-two-million Iranians are eligible to vote in Friday's election, according to Iran's Interior Ministry, and official results are expected to be announced less than 24 hours after polls close Friday evening.