Iranian reform protestors pelt police with stones

Opponents of Mahmoud Ahmadinejad have clashed with police in the heart of Iran's capital, pelting them with rocks and setting fires in the worst unrest in Tehran in a decade.

They accused the hardline president of using fraud to steal election victory from his reformist rival.

The angry confrontations, including stunning scenes of masked rioters tangling with black-clad police, pushed the self-styled reformist movement closer to a possible moment of truth - whether to continue defying Iran's powerful security forces or, as they often have before, retreat into quiet dismay and frustration over losing more ground to the Islamic establishment.

However, for at least one day, the tone and tactics were more combative than at any time since authorities put down student-led protests in 1999. Young men hurled stones and bottles at anti-riot units and mocked Mr Ahmadinejad as an illegitimate leader.

The reformists' new hero, Mir Hossein Mousavi, declared himself the true winner of Friday's presidential race and urged backers to resist a government based on "lies and dictatorship".

Authorities, too, pushed back with ominous measures apparently seeking to undercut liberal voices: jamming text messages, blocking pro-Mousavi websites and Facebook and cutting off mobile phones in Tehran.

The extent of possible casualties and detentions was not immediately clear. Police stormed the headquarters of Iran's largest reformist party, the Islamic Iran Participation Front, and arrested several top reformist leaders, said political activists close to the party.

Mr Mousavi did not appear in public, but warned in a web message: "People won't respect those who take power through fraud."

Many backers took this call to the streets and thousands of protesters - mostly young men - roamed Tehran looking for a fight with police and setting rubbish bins and tyres ablaze.

Pillars of black smoke rose among the mustard-coloured apartment blocks and office buildings in central Tehran. In one side road, an empty bus was engulfed in flames.

Police fought back with clubs, including mobile squads on motorcycles swinging truncheons.

The scuffles began when protesters gathered outside the interior ministry as officials announced the final election results showing a nearly 2-1 landslide for Mr Ahmadinejad.

Demonstrators chanted: "The government lied" and waved the ribbons of Mr Mousavi's "green" movement - the signature colour of his youth-driven campaign.

"I won't surrender to this manipulation," said a statement on Mr Mousavi's website.

"The outcome of what we've seen from the performance of officials ... is nothing but shaking the pillars of the Islamic Republic of Iran's sacred system and governance of lies and dictatorship."

Many sections of central Tehran appeared calmer after midnight, with no signs of open clashes. But the mood remained tense. Large groups of riot police patrolled the streets, moving along drivers who had been honking their horns in apparent protest.

The door for possible compromise was closed by Iran's supreme leader, Ayatollah Ali Khamenei, who could have used his near-limitless powers to intervene in the election dispute.

However, in a message on state TV, he urged the nation to unite behind Mr Ahmadinejad, calling the result a "divine assessment".

The US has refused to accept Mr Ahmadinejad's claim of a landslide re-election victory said it was looking into allegations of election fraud.

Secretary of State Hillary Clinton said she hoped the outcome reflected the "genuine will and desire" of Iranian voters.

At a joint appearance with Mrs Clinton, Canadian foreign affairs minister Lawrence Cannon said his country was "deeply concerned" by reports of irregularities in the election.

Past Iranian elections were considered generally fair. In 2005, when Mr Ahmadinejad was first elected, the losing candidates claimed irregularities at the polls but the charges were never investigated.

"The majority of Iranians are certain that the fraud is widespread," said Tehran-based analyst Saeed Leilaz. "It's like taking 10 million votes away from Mousavi and giving them to Ahmadinejad."

Whether this is enough to spawn a sustained opposition movement remains an open question.

Much depends on how much they are willing to risk. The heartland of Iran's liberal ranks is the educated and relatively affluent districts of north Tehran. It is also the showcase for the gains in social freedoms that began with the election of President Mohammad Khatami in 1997: make-up, internet cafes, headscarves that barely cover hair and satellite dishes that are technically illegal.

The ruling clerics tolerate all that to a point - part of a tacit arrangement that the liberties stay as long as reformists remain politically meek.

Mr Ahmadinejad accused the foreign media of producing coverage that harmed the Iranian people, saying "a large number of foreign media ... organised a full-fledged fight against our people".

Authorities also called foreign journalists with visas to cover the elections and told them they should prepare to leave the country.

Mousavi called on his backers to avoid violence, but he is still talking tough about pressing his claims of election fraud. He claims the polls closed early but has not fully outlined all of his fraud allegations.