Pro-government demonstrations are taking place in several Iranian cities in response to a recent spate of opposition rallies.
Reports say thousands of people have taken part.
At least eight people were killed in opposition demonstrations on Sunday, and 300 were reportedly arrested.
The BBC reports it was one of the most violent protests since the election in June when President Mahmoud Ahmadinejad was re-elected. The opposition claims the poll was rigged.
Iranian authorities have accused western powers of stirring up the protests.