Iran marked the anniversary of the 1979 Islamic revolution yesterday as its hardline president Mahmoud Ahmadinejad taunted Western powers with the defiant boast that Iran was now "a nuclear state".
He said Iran would not be bullied by international pressure into curbing its nuclear ambitions and had already produced the first batch of uranium enriched to a level that could equip it with a nuclear weapons capability.
Anti-government protesters had hoped to use revolution day celebrations for a big display of defiance, but a massive security clampdown choked off the threat of major disruption. There were clashes with police at several locations across Tehran, with tear gas and paintballs fired to disperse crowds chanting opposition slogans. Opposition websites claimed at least one person was shot dead by security forces.
Leading figures from within the opposition camp were reportedly harassed, including the elderly cleric Mehdi Karroubi, who stood in last June's disputed elections. He was attacked by hardliners who broke the windows of his car and had pepper sprayed on him.
Zahra Rahnavard, the wife of Mirhosein Moussavi, the other presidential challenger, also reportedly suffered a beating when she appeared in the streets, while Zahra Eshraghi, the reformist granddaughter of Ayatollah Khomeini, the founder of the Islamic Republic, was briefly detained.
Videos purportedly of protesters shouting "Death to the dictator" in Isfahan Mashhad and other Iranian cities were posted on opposition websites. But posts on Twitter from Iran reported that while counter-demonstrations took place in locations such as Tehran's Saddeqiya Street, efforts to move into the heart of the city were pushed back by armed Basiji militias on motorbikes.
The Supreme Leader Ayatollah Ali Khamenei had warned reformists in the "Green movement" that they would suffer a "punch in the mouth" if they wrecked the official celebrations and it seems many, perhaps intimidated by the executions of two leading dissidents, heeded the threat. Internet disruptions, including the shutdown of Google's email service in Iran, may also have hampered the opposition's ability to organise.
Huge crowds – state television said numbering "tens of millions" – carrying flags and posters of Ayatollah Khomeini, the founder of the Islamic republic, thronged the streets leading to the Azadi (Freedom) monument where Mr Ahmadinejad delivered the traditional Revolution day address.
But any sense of victory in the pro-government camp is likely to be tempered by a continuing nervousness at the ongoing divisions in the regime and an opposition movement that can only be contained with huge numbers of security forces. Nader Mousavizadeh, an expert on Iran with the London-based International Institute for Strategic Studies, said the regime could draw limited comfort from its show of power. "There are two explanations," he said. "Either you believe the last six months of repression have convinced the green movement that they like the regime, or you believe there was an unprecedented security operation in force."
Mr Mousavizadeh said the regime remained "deeply deeply divided" on the opposition, on the economy and on the nuclear issue. "These divisions will not end now. There are unresolved tensions and they have not gone away".
How much genuine public support for the hardline faction that controls the levers of power remains difficult to guage even from yesterday's turnout. The celebration is a public holiday in Iran, and many of those who attend the rally are bused in from outlying areas, lured by free gifts or food. Many Iranians also attend out of loyalty to the values of the revolution even if they are highly critical of the country's current leadership.
In his address to the nation the President said nuclear physicists had successfully enriched the first batch of uranium to a grade of 20 per cent purity.
"The first package of 20 per cent fuel was produced and provided to the scientists," he said without specifying how much uranium had been enriched to this level. Iran has only previously enriched to only 3.5 per cent and the move to 20 per cent is viewed with alarm in Western capitals because it signals that Iran is moving closer to the point where it can build nuclear bombs.
Gordon Brown last night said patience was wearing thin with Iran. "Iran can either pursue a civilian nuclear programme, respect human rights and earn the trust and respect of the international community," the Prime Minister said. "Or it can move ahead with its nuclear weapons programme, trample on human rights and be isolated and ostracised on the wrong side of history."
Catherine Ashton, the European Union's foreign policy chief, criticised Iran's record on human right.