Mahmoud Ahmadinejad was re-elected as Iran's president on Saturday, winning 62.6 per cent of the vote, while his rival Mir Hossein Mousavi denounced the victory as a "dangerous charade."
Mousavi, who was Ahmadinejad's closest rival, took 33.75 per cent of the vote in the contest that appeared to divide urban against rural voters.
Following news of the election win, Iran's supreme leader, Ayatollah Ali Khamenei — who has final say on all state matters — thanked the people for their record 85 per cent participation and warned opposition candidates to avoid what he described as "provocative" behaviour.
"The chosen and respected president is the president of all the Iranian nation," Khamenei said in a statement read on state television, adding that all Iranians "must unanimously support and help him."
Still, Mousavi, who is Iran's former prime minister, was not yet conceding defeat, and claimed voting irregularities.
"I'm warning I will not surrender to this dangerous charade. The result of such performance by some officials will jeopardize the pillars of the Islamic republic and will establish tyranny," Mousavi said in a statement to Reuters.
"There are going to be some pretty difficult days ahead," the CBC's Nahlah Ayed reported from Tehran on Saturday.
"It's a very tense city right now," she said, adding that police were in the streets wearing riot gear.
"Last night and also today there were clashes," Ayed said.
Demonstrators were seen in Tehran wearing Mousavi's trademark green colour and chanting. As well, there were reports that protesters had set fire to tires outside the Interior Ministry in the city.
Witnesses told The Associated Press that a commercial bank elsewhere in the capital had been set on fire.
More than 470 people had sought to join the presidential race, but only Ahmadinejad and three rivals were cleared.
The rowdy campaign reached a crescendo in the past few days with duelling rallies by supporters of Ahmadinejad and Mousavi that drew tens of thousands into the streets of Tehran.
Ahmadinejad maintained broad support among rural and working poor voters, while Mousavi took much of the middle-class and urban vote.
The newly elected president will serve a four-year term.
