A reformist Web site in Iran said clashes erupted between security forces and opposition supporters in central Teheran on Saturday.
The Rah-e-Sabz site said forces including the Revolutionary Guard and paramilitary Basij forces confronted demonstrators on Saturday and broke the windows of cars that were honking horns in protest.
Iran is marking the first 10 days of the Islamic month of Moharram, a time of mourning rituals for a revered Shi'ite saint.
The period culminates Sunday with Ashoura - a day that coincides with the seventh day since the death of Iran's most senior dissident cleric, Grand Ayatollah Hossein Ali Montazeri. More memorials and possible protests are expected.