Iran's leaders scored home a point by stifling opposition protesters on the anniversary of the 1979 Islamic revolution, but Tehran's nuclear challenge is a doubtful victory on the international front.

A large police presence ensured that Thursday's celebrations did not degenerate into a repeat of the violent December 27 protests against President Mahmoud Ahmadinejad in which at least eight people were killed, plunging Iran into one of its worst crises since the revolution.

Opposition websites reported scattered demonstrations, which were quickly choked by anti-riot forces who carried out many arrests according to accounts told to AFP.

But the scale of the protests was impossible to gauge, because foreign media were banned from reporting anything but Ahmadinejad's defiant nuclear speech at Tehran's Azadi (Freedom) Square.

To interrupt the cycle of protests that have erupted since Ahmadinejad's June re-election, authorities virtually paralysed the Internet and telephone texting services used by the opposition to communicate with supporters.

Foreign satellite channels that are widely watched in Iran also were scrambled.

Some of the opposition's main leaders were attacked on Thursday to prevent them from leading anti-government protests, opposition websites reported.

The virtual news vacuum enabled authorities to show off their popularity with the hundreds of thousands — millions according to official figures — who took part in the officially organized processions across the country.

"The bombardment of propaganda by enemies through their websites and networks … had no impact but created more solidarity," as throngs took part in state-sponsored celebrations, Friday prayer leader Kazem Sedighi was able to boast to worshippers in Tehran.

In a massive crackdown following the post-election violence, authorities have arrested thousands, including journalists and reformist politicians, in a massive crackdown.

Two people have been hanged and nine are on death row.

Iranian authorities "gained a tactical victory (against the opposition)," said former French ambassador to Iran, Francois Nicoullaud.

It was "a rather easy victory … taking into account the means at its (the regime's) disposal," Nicoullaud told AFP in Paris.

Ahmadinejad took a defiant note before the crowds on Thursday, boasting that Iran was now a nuclear nation.

He said that while Iran did not wish to produce nuclear weapons, it did have the capacity to produce highly enriched uranium.

Iran had previously enriched uranium to just 3.5 percent but has started enriching it to the higher level required for a Tehran medical research reactor after snubbing a UN-drafted plan for the nuclear fuel to be supplied by France and Russia.

Even before Ahmadinejad's speech, the West had already warned that Tehran would soon be slapped with new sanctions.

The European Union was ready to announce its own sanctions against Iran within "days or weeks" if the UN Security Council fails to do so, according to Finnish Foreign Minister Cai-Göran Alexander Stubb.

On Wednesday, the US Treasury Department already imposed an asset freeze on an Iranian Revolutionary Guard Corps commander and four subsidiaries of a construction firm owned or controlled by the elite force.

The West suspects Iran of using its nuclear programme as a cover for efforts to build the atomic bomb, a charge Iran strongly denies.

Western governments have stepped up the pressure on Iran since it announced on Tuesday it had begun work to enrich uranium to 20 percent, which it says is for the Tehran research reactor that makes medical isotopes.

"This new gesture of challenging the international community can only accelerate the economic and political sanctions, leading to an isolation and weakening of Iran," said a Western diplomat, speaking on condition of anonymity.

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