Around midnight in west Tehran's Ferdows neighborhood, residents took to the streets, chanting slogans against the president and setting trash cans on fire. In the Villa district in downtown Tehran, residents marched chanting, "We fight! We die! But we'll get our votes back."
The election commission swiftly declared Ahmadinejad the winner over Mousavi after a hotly contested race. But even before Friday's voting ended, Mousavi and another candidate, Mehdi Karroubi, had complained of massive vote-rigging.
When vote tallies were announced showing Ahmadinejad with more than 63% of the vote, rowdy riots and unrest erupted throughout the capital and in Esfahan, Tabriz, Orumieh, Rasht and Shiraz.
There were conflicting reports Sunday about whether Mousavi was under house arrest. Officials denied that he was, but Mashallah Shamsolvaezin, a confidant, said Mousavi and his wife, Zahra Rahnavard, were under house arrest and cut off from most communications.
Through a website, Mousavi called on supporters to refrain from violence and "harming themselves."
He also announced plans to formally appeal the election results through the Council of Guardians. But there seemed little likelihood that an appeal would succeed because the council is appointed by Ayatollah Ali Khamenei, Iran's top political and religious leader, who made a speech on state television strongly praising Friday's vote.
A Mousavi campaign official said his office had requested permission to hold a rally in Tehran today so he could make a speech to try to cool the passions of his supporters.
Another presidential contender, Mohsen Rezai, the sole conservative running against Ahmadinejad, said he recognized the legitimacy of the vote.
"A person who has become president through legal procedures is the president of all Iranian people," the former Revolutionary Guard commander said in a statement.
Western leaders have voiced concern about the unrest and allegations of fraud and civil liberties violations. But U.S. officials remained cautious, worried that their words could taint the opposition as American stooges.
Vice President Joe Biden said Sunday that the Obama administration would "wait and see" before drawing a conclusion about the events in Iran. Still, he expressed skepticism about the vote count.
"It sure looks like the way they're suppressing speech, the way they're suppressing crowds, the way in which people are being treated that there's some real doubt about that," he said in an interview with NBC News.
