Supporters of the defeated presidential candidate Mir-Hossein Mousavi staged protests in the Iranian capital on Monday during celebrations of national Student Day, Iranian and western media reported.
Student Day, celebrated this year on December 7, marks the day three Tehran University students were killed during protests against then U.S. vice-president Richard Nixon's visit to Iran in 1953.
Iran's semi-official FARS new agency said Mousavi supporters threw bottles and stones at the supporters of President Mahmoud Ahmadinejad and a clash broke out.
The official IRNA news agency reported clashes between opposition activists and police.
The Tehran Times quoted a police statement, issued ahead of the celebrations, which says that "any gathering or ceremony outside the specified places will be considered illegal" and police will deal with it "as its legal duty."
According to BBC, authorities also banned media coverage of Student Day by foreign journalists. Accreditation of all foreign media was suspended from December 7 to December 9. Journalists are also banned from leaving their bureaus during that period.
Ahmadinejad's re-election triggered mass protests by Mousavi's supporters in June. At least 30 people were reported to have been killed and about 1,000 arrested in post-election violence in the capital Tehran and some other cities, in Iran's most severe unrest since the 1979 Islamic Revolution.
MOSCOW, December 7 (RIA Novosti)
