Greek police clash with students in Athens as thousands march on anniversary of death of Alexandros Grigoropoulos

Police fired teargas at rioters who threw rocks and firecrackers in central Athens as thousands gathered to mark the first anniversary of the police shooting of a teenager.

Clashes broke out as about 3,000 people, mostly students, anarchists and leftists, began a march to parliament. More protests were expected tomorrow. An evening memorial service was planned in the Exarchia district, where 15-year-old Alexandros Grigoropoulos was shot dead.

Violence also broke out in Thessaloniki, Greece's second-largest city, where demonstrators threw petrol bombs at police and smashed the front of a Starbucks cafe.

More than 6,000 police were deployed across greater Athens amid fears that the demonstrations under way in the capital and other Greek cities would turn increasingly violent. Concern was heightened by reports that far-left groups and anarchists from other European countries have travelled to Greece for the protests.

Grigoropoulos was shot by a policeman on the evening of 6 December 2008, in Exarchia, a central Athens neighbourhood of bars and cafes popular with anarchist groups. Within a few hours of his death, riots spread from the capital to several cities, taking the government by surprise. An embattled police force took a passive approach as rioters looted and burned shops in violence that lasted two weeks.

The new socialist government, which has faced a spate of attacks by far-left and anarchist groups, since coming to power in October, has vowed not to tolerate any violence during today's anniversary.

Police yesterday detained about 160 youths and raided what they described as a firebomb-making hideout in the district of Keratsini, near the port of Piraeus. A memorial gathering last night at the spot where Grigoropoulos was killed began peacefully, although clashes broke out in the area later between rock-throwers and riot police. Police arrested 14 people, including five Italians and three Albanians.

Dozens of police, some in riot gear and others on motorbikes, stood guard throughout the district on Saturday night. Apart from the brief clash, the area was quiet, with heavy rain helping keep people off the streets.

Greece's civil protection minister, Michalis Chrisochoidis, who is also in charge of the police, said earlier this week that people had been right to demonstrate against the teenager's death, but further riots would not be tolerated.

"Without doubt (Grigoropoulos's death) was an act of extreme police violence and misconduct that has scarred our collective memory," Chrisochoidis said. "Young people were right to take to the streets to express their outrage. But we will not tolerate a repeat of the violence and terror in the centre of Athens and other cities. We will not surrender Athens to vandals."