Iran's Supreme Leader Ayatollah Ali Khamenei has said the nation "will not yield to pressure" over a disputed presidential election.
Several people have been killed in days of street protests since the 12 June poll returned Mahmoud Ahmadinejad to the presidency.
Violence erupted after protesters claimed the elections were rigged.
Restrictions have been placed on the BBC and other foreign news organisations in Iran. Reporters are not allowed to cover unauthorised gatherings or move around freely, but there are no controls over what they can say.
Jeremy Bowen reports from Tehran.
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