Iran opposition: Over 200 'arrested' in Tuesday protest
Iran's opposition says more than 200 people were arrested on Tuesday while trying to protest in Tehran.
Opposition websites said security services rounded up protesters in several locations in the capital and were helped by police in plain clothes.
Another 40 people were said to have been detained in the city of Isfahan.
Opposition groups had called for rallies over the reported imprisonment of their leaders - Mir Hossein Mousavi and Mehdi Karroubi.
The two men had been placed under house arrest several weeks ago as authorities cracked down on protests staged in solidarity with the uprisings in Tunisia, Egypt and elsewhere.
Their families say that on Monday they were taken to prison, although the government denies this.
Riot police and militia on motorcycles broke up attempts by a number of opposition supporters to protest in various parts of Tehran on Tuesday.
One website said eyewitnesses had reported 30 arrests on Felestin Street alone.
"Masked officers arrested men and women and put them into black vans and continued beating them even after they were put in the van," the Human Rights House of Iran reported.
There has been no independent confirmation of the number of arrests.
But the BBC has learned that Fakhrosadar Mohtashami, the wife of former minister Mostafa Tajzadeh, was one of those detained.
A relative told BBC Persian that Ms Mohtashami is being kept in Evin Prison and has not been allowed contact with her family for the time being.
No Iranian officials have acknowledged Tuesday's protests, and they were ignored by Iranian state media.
Both Mr Mousavi and Mr Karroubi ran as opposition candidates in the disputed June 2009 presidential election.
Mr Mousavi said he was the actual winner and President Mahmoud Ahmadinejad was only re-elected through a rigged vote.
Hundreds of thousands of opposition supporters then took part in marches that were crushed by the security forces.