The Guardian Council in Iran is due to give its definitive report on Sunday on the fairness of the recent elections, but it has already said the results should stand.
The BBC's Jeremy Bowen said this put a lot of pressure on the opposition.
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. The BBC's Middle East Editor Jeremy Bowen reports from Tehran.