ATHENS, Dec. 6 (Xinhua) -- Violent scuffles broke out during a demonstration in downtown Athens on Thursday between protesters and anti-riot police.
The demonstration, staged by students' unions and Leftist parties, is to mark the 10th anniversary of the killing of a teenager by police fire.
Groups of hooded youth pelted rocks and petrol bombs at policemen who responded with tear gas and stun grenades.
A yet unidentified number of protesters were detained, according to Greek national news agency AMNA.
Later in the day, another protest is due to be held near the place where the 15-year-old high school student, Alexandros Grigoropoulos, was shot dead on Dec. 6, 2008 by a policeman who was convicted to life imprisonment.
The death of Grigoropoulos was followed by a string of violent clashes across Greece for two weeks in protest of police violence. Its anniversary has been marred by violent incidents every year.
Some 5,000 officers were deployed across the city center of Athens on Thursday to monitor the protests, according to the police.