Police used batons and teargas to break up an opposition protest in central Tehran on Wednesday, while huge crowds staged a noisy anti-US rally nearby to mark the storming of the American embassy by students 30 years ago.

Witnesses said the violent clashes occurred at Haft-e-Tir square in the heart of the capital when riot police armed with batons and firing teargas moved in on a crowd of several hundred opposition supporters staging a protest. The protesters, who were chanting "Death to the dictator," refused to disperse and dozens were beaten or arrested. Groups of pro-government hardliners also gathered at the square chanting "Death to America."

Wednesday'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 November 4, 1979 -- just months after the Islamic revolution toppled the US-backed shah.

The students, who took 52 American 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.

The two countries broke diplomatic ties after the event, which have yet to be restored.