It was meant to be a highlight of the Iranian revolutionary calendar, a day of mass rallies sponsored by the government to showcase contempt for America and the West.
But the official commemoration of the 30th anniversary of the storming by students of the US embassy in Tehran and the start of the 1979 hostage crisis was hijacked by the opposition yesterday – for their biggest show of strength in months.
Violence occurred on some of the main thoroughfares of the capital and other Iranian cities after thousands defied messages sent to mobile phones warning them to stay at home or face prosecution. Dozens of activists had been arrested and the main metro stations closed, but undeterred, people poured onto the streets to show their disapproval of the hardline President Mahmoud Ahmadinejad and his clerical backers, a reflection of the political turmoil still raging in Iran.
In response, Revolutionary Guards and Basijis, the feared volunteer militias used to suppress dissent, were deployed in a crackdown which the White House last night described as "worrying". Batons were used to club protesters and tear gas sprayed with what witnesses described as "brutal" force. Opposition groups reported that live ammunition was used in shots fired at one group of demonstrators and that there were injuries, but this could not be verified.
Iran's protest movement has not been much in evidence lately, having been driven underground by the rounding up and jailing of hundreds of opposition figures after the mass unrest provoked by the disputed June elections. But yesterday's events will remind the regime that public discontent remains very close to the surface and that the so-called "green" movement is a long way from being moribund.
Iranian bloggers and Twitterers reported an unprecedented level of open denunciation of regime figures during yesterday's events. In Tehran, but also in cities like Rasht and Tabriz, the ritual "Death to America" chants expected on such occasions were matched by chants of "Down with the Dictator".
Video clips posted on pro-reform websites apparently filmed yesterday, showed posters bearing the image of the Supreme leader Ayatollah Khamenei being trampled, which is tantamount to heresy. Others showed large crowds marching purposefully through the wide main streets of the capital chanting "Khamenei is a murderer – his rule is null and void" – a sentiment that it is unheard of to utter in public. In another clip people shouted: "Obama: you're either with them or with us!"
In Washington, the US President used the anniversary to urge Iran's leaders to move beyond "suspicion, mistrust and confrontation". Iran "must choose" he said. "We have heard for 30 years what the Iranian government is against, the question, now, is what kind of future it is for."
While posters of the defeated presidential candidate Mirhosein Mousavi, were on show, it was Mehdi Karroubi the elderly cleric who has replaced Mr Mousavi as the most outspoken opposition figure, who was met with an ecstatic reception when he appeared at a march near Tir 7 square in his trademark white turban. "Karroubi, champion, attend to the cries of Iran!" went one chant, while others just repeated his name over and over. According to Mr Karroubi's website, a tear gas canister was fired, injuring his bodyguard who had to be taken to hospital.
In other locations phalanxes of Basij militias on motorbikes revved their engines menacingly to put off the passing marchers, a reminder of the violence meted out during the summer protests by thugs ferried about the cities on the back of motorbikes.
According to IRIB, the state TV station, the only rally was the official one outside the former US embassy, the scene of the 444-day-long hostage siege, and locally referred to as the "den of spies". Thousands of people turned out for this, many carrying anti-US posters. Some banners proclaimed: "We are ready to sacrifice our blood for Khamenei." Away from the official cameras however, people were reportedly chanting: "The Russian embassy is a den of spies," a reference to Russia's support for Mr Ahmadinejad.