Thousands of Iranians have come out onto the streets of Tehran today to stage anti-US rallies marking the storming of the American embassy by students 30 years ago.

Wednesday's anniversary, which has turned into a cornerstone of the regime, marks the capture by radical Islamist students of the US embassy compound on 4 November 1979, shortly after the Shah was deposed. The students, who took 52 US diplomats hostage, said they were responding to Washington's refusal to hand over the ousted Shah, Mohammad Reza Pahlavi. The hostages were released after 444 days. The two countries broke diplomatic ties after the event, which have yet to be restored.

President Barack Obama said in a statement marking today's anniversary of the event that Iran "must choose" now whether to open the door to opportunity and prosperity.

In other parts of Tehran, there are also reports of skirmishes between riot police armed with batons and opposition supporters attempting to use the rally to stage an anti-government protest. Police fired teargas into the crowds chanting "Death to the dictator". Witnesses say shots were also fired when the protesters refused to disperse.

Opposition leaders Mir Hossein Mousavi and Mehdi Karoubi have led several demonstrations against President Mahmoud Ahmadinejad, who they claim committed electoral fraud in last June's presidential elections.