Police fired tear gas and made several arrests, AFP news agency reported, citing witnesses.
A report from Reuters quoted one witness as saying police had used batons to disperse demonstrators chanting "death to dictators".
Reformist leaders had urged supporters to turn out to mark 30 years since the seizure of the US embassy.
But Iran´s Revolutionary Guards had warned opposition groups not to hold protest rallies.
Since June, Iranian opposition supporters have been staging protests over elections they say were rigged to ensure the re-election of President Mahmoud Ahmadinejad.
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