Iranian riot police have clashed with mourners who gathered at a cemetery to commemorate protestors killed in post-election violence.

Police used sticks, batons and belts on some of the hundreds of people at the graveyard where protestors are buried.

Police later forced opposition leader Mir-Hossein Mousavi to leave and arrested several mourners.

The cemetery became a flashpoint as crowds gathered to mark the 40th day since the death of Neda Agha-Soltan, a young woman who came to symbolise the protest movement against the re-election of President Mahmoud Ahmadinejad.

State TV has said that police used tear gas to disperse crowds from the grave of Neda Agha Soltan, whose death became a symbol of post-election unrest.

Witnesses said about 150 police and some members of the Islamic Basij militia were in and around the Behesht-e Zahra cemetery south of Tehran.