Meanwhile, thousands of Iranians staged a noisy anti-US rally in Tehran to mark the 30th anniversary of the storming of the US embassy by students.
US President Barack Obama said in a statement marking the anniversary of the event, which sparked decades of hostility between the US and Iran, that the Islamic republic 'must choose' whether to open the door to opportunity and prosperity.
Huge crowds from early morning descended on the embassy complex in central Tehran, chanting slogans such as 'Death to America' and 'Death to Israel'.
They also smashed up posters of the US 'Uncle Sam' symbol and chanted 'The blood in our veins is a gift to our leader' - a reference to Iranian supreme leader Ayatollah Ali Khamenei.
The crowd was constantly being swelled by people arriving on foot and by bus, witnesses said.
About 1km away at Haft-e-Tir square in the heart of the capital, riot police armed with batons and firing tear gas moved in as several hundred opposition supporters attempted to stage an anti-government protest.
Witnesses said the protestors, who were chanting 'Death to the dictator,' refused to disperse and dozens were beaten and arrested.
Since June, opposition supporters have been staging protests at every opportunity in Tehran against the re-election of Iranian President Mahmoud Ahmadinejad. Mr Ahmadinejad was relected in a presidential vote opponents claim was massively rigged.
Today's anniversary, which has turned into a cornerstone of the Islamic regime, marks the capture by radical Islamist students of the US embassy compound on 4 November, 1979, just months after the Islamic revolution toppled the US-backed shah.
The students, who took 52 US diplomats hostage and held them for 444 days, said they were responding to Washington's refusal to hand over the deposed shah, Mohammad Reza Pahlavi.
