The Iranian government declared President Mahmoud Ahmadinejad the winner of this week’s election with 62.63 per cent support, results disputed by the leader’s main rival as tensions between the two sides boiled over in Tehran.

Ahmadinejad’s opponent, reformist Mir Hossein Mousavi, trailed with only 33.75 per cent of the vote, despite what many experts believed would be a close election.

The final vote tally led to clashes between riot police and Mousavi supporters on the streets of Tehran Saturday.

Protesters, many wearing the green colours of the reform-minded Mousavi’s campaign, set tires on fire outside the Interior Ministry, which ran Friday’s elections, despite increased security around the building.

Police beat the demonstrators with clubs and smashed cars while officers on motorcycles chased protesters through the streets.

Some protesters retaliated by throwing stones at police.

On one of Tehran’s main streets, about 300 people formed a human chain chanting, “Ahmadi, shame on you. Leave the government alone.”

Mousavi said he believed the election was rigged and threatened to challenge the results, which he called “treason.”

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