Supporters of Mir Hossein Mousavi are planning a new demonstration in Tehran in protest at what they see as a fraudulent presidential poll in Iran.
The planned rally comes after overnight raids on university dormitories in several Iranian cities and as two pro-reform figures were arrested.
Heavy restrictions have now been placed on the BBC and other foreign news organisations. Reporters are not allowed to cover unauthorised gatherings or move around freely in Tehran - but there are no controls over what they can say.
Jon Leyne reports from Tehran.
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