Iranian opposition supporters have held protests in several parts of Tehran, on the anniversary of the arrest of two of the movement's main leaders.
Mir Hossein Mousavi and Mehdi Karoubi were put under house arrest last year after backing a major protest.
Security forces were deployed throughout the capital after opposition groups called for people to take to the streets to mark the anniversary.
A number of people were detained in one of the city's main squares.
Elsewhere security forces staged random searches for mobile phones, BBC Persian understands.
Mr Mousavi, a former prime minister, and Mr Karoubi, a former speaker of Parliament, were the figureheads of the opposition Green Movement, which was trying to show support for "Arab Spring" protests.
Since their detention, their whereabouts are not known.
The Iranian authorities had warned they would stop any public move to mark the anniversary.
Human rights groups say that in recent days Iran's authorities have carried out a series of arrests of journalists and bloggers.
They also held anyone with links to the foreign media, as part of a strategy to restrict debate and prevent any kind of protest.
Internet users in Iran have been unable to access foreign email services.