Iranian police have fired tear gas at opposition supporters participating in a rally in the centre of the capital, Tehran, called in solidarity with the popular uprisings in Egypt and Tunisia.
A BBC producer, who was affected by the gas, said there had been severe clashes and described a scene of “total chaos”.
There were also reports of protests in the cities of Isfahan and Shiraz.
Earlier, the police placed opposition leader Mir Hossein Mousavi under house arrest, according to his website.
It said the move was intended to prevent the former prime minister attending the march in Tehran, which the authorities had prohibited. The road leading to Mr Mousavi’s house was also blocked by police vans.