TEHRAN, Iran — A pivotal presidential election in Iran ended in confusion and confrontation early this morning as both sides claimed victory and officers fired tear gas to disperse a cheering crowd outside the campaign headquarters of opposition candidate Mir Hossein Mousavi.
Just two hours after the polls closed Friday night, Iran's state-run news agency said President Mahmoud Ahmadinejad had won the election in a landslide. But Mousavi, his main rival, charged that there had been voting "irregularities."
"I am the absolute winner of the election by a very large margin," Mousavi said during a news conference with reporters Friday night, adding: "It is our duty to defend people's votes. There is no turning back."
An hour later, the state news agency reported that Ahmadinejad had won the election with 69 percent and Mousavi had 28 percent. As the election commission announced new totals throughout the night, the numbers changed slightly, but the wide lead by Ahmadinejad did not.
The election commission is part of the Interior Ministry, which Ahmadinejad controls. Some lawmakers were already congratulating Ahmadinejad, and some of his supporters were celebrating in the streets, the agency said.
The conflicting claims, coming after an extraordinary campaign that saw vast street demonstrations and vitriolic televised debates, seemed to undermine the public legitimacy of the vote and to threaten unrest. In recent days, Mousavi's supporters were predicting a massive victory, citing voter surveys.
President Barack Obama said the "robust debate" during the campaign suggests change may come to Iran.
"You're seeing people looking at new possibilities," Obama said. "And whoever ends up winning the election in Iran, the fact that there's been a robust debate hopefully will help advance our ability to engage them in new ways."
Some analysts warned that Mousavi's supporters might take to the streets to protest today, despite a warning against any demonstrations by the deputy commander of the Iranian national police, Ahmadreza Radan.
When Mousavi's youthful supporters gathered after midnight outside his Tehran headquarters to celebrate his claim to victory, officers quickly dispersed them with tear gas, said Milad Afsarzadeh, a Mousavi campaign official inside the building.
He and other witnesses to the brief melee said it was unclear whether the officers were police or members of the Baseej, a paramilitary force of volunteers organized by the Revolutionary Guards and feared by student demonstrators. No serious violence was reported.
Ahmadinejad, who has been president since 2005, did not make any immediate statement, but his supporters pointed to the Interior Ministry's official tally to claim victory.
Mousavi's supporters charged that officials were trying to steal the election and cut off alternative sources of information. For several hours during the balloting, they said, international phone lines to Tehran were down and text messaging — which Mousavi's supporters had used to organize street rallies — was blocked. Members of the Baseej reportedly seized a building in North Tehran that housed several Web sites supporting Mousavi, which were shut down.
Fraud has been a prominent concern for Mousavi's campaign, with many of his allies warning that Ahmadinejad could use the levers of state — the military, the Revolutionary Guard, and the Baseej — to cajole or intimidate voters, or even engage in outright fraud. In 2005, Mehdi Karroubi, who is also a candidate in this election, accused the Baseej of rigging the vote in Ahmadinejad's favor after he was eliminated in the first round.
Mousavi called on the country's supreme leader, Ayatollah Ali Khamenei, to help the country reach a "favorable conclusion." Khamenei, who has final authority over affairs of state, appears to be the only figure who could mediate between the two camps in the event of an open confrontation over the vote.
While casting his ballot Friday, Khamenei had said that people were using texting to spread rumors, but it is unclear if that is why the services were shut down.
The discord capped a day of long lines at polling places across the capital. "We haven't voted in 10 years time," said Giti Ghioshfar, who was waiting with her husband to cast their ballots for Mousavi. "We are here because we want more freedom."
In Shahr-e Rey, south of Tehran, voter Ali Badiri said that young women without headscarves had been dancing in the streets over Mousavi's candidacy. "I'll vote for Ahmadinejad, because if Mousavi wins, they will be dancing naked next week," he said.
"We don't want to change Iran," said Abdollah Khalili, another Ahmadinejad voter. "We want this system to remain the way it is."