ATHENS: Protesters hurled rocks and burning garbage at police Sunday as violence erupted during a march to mark the first anniversary of the police shooting of a teenager, whose death sparked massive riots.

Police fired tear gas at scores of hooded youths in central Athens, as several thousand demonstrators marched to commemorate the death of 15-year-old Alexandros Grigoropoulos.

The rioters smashed bank windows, overturned trash bins and hurled rocks and fire crackers at riot police. Authorities said 48 people were detained for public-order offenses. At least five protesters were injured in the clashes.

Police on motorcycles chased rioters amid scenes of chaos at Athens' main Syntagma Square, with youths punching and kicking officers pushed off their bikes.

At Athens University, masked protesters broke into the building and pulled down a Greek flag, replacing it with a black-and-red anarchist banner.

Violence also broke out in Thessaloniki, Greece's second-largest city, where youths threw petrol bombs at police, set fire to several cars and smashed 10 storefronts, including a Starbucks cafe. At least 20 people were detained in the northern city.

More than 6,000 police had been deployed across greater Athens in anticipation that demonstrations would turn violent. Protests were held in the capital and several other Greek cities.

Concern was heightened by reports that far-left groups and anarchists from other European countries have traveled to Greece to join the marches.

Ahead of Sunday's clashes, police detained 160 people following minor clashes in central Athens and a raid on a cafe, where police seized sledgehammers and firebomb-making equipment.

Grigoropoulos was killed by a policeman's bullet on the evening of Dec. 6, 2008. Within a few hours of his death, riots spread from the Greek capital to several cities across the country, with police apparently powerless to prevent youths from smashing, looting and burning stores in violence that continued for two weeks.

The new Socialist government, which came to power in October and has been confronted with a surge in armed attacks by far-left and anarchist groups after last year's shooting, and had vowed a zero-tolerance approach to violence at Sunday's commemorations.