Police in Greece fired several rounds of teargas to disperse rioting protesters, as thousands marched in Athens to mark the anniversary of the police killing of a teenager.
The shooting unleashed the country's worst riots in decades last year.
Eyewitnesses say hooded youths broke from a march of more than three thousand people on Sunday to smash shop windows, set fire to garbage bins and hurl stones at police.
In Thessaloniki, Greece's second-largest city, demonstrators threw petrol bombs at police, who responded with teargas. They say about 150 foreign anarchists arrived from Italy, France and other European countries.
Dozens of schools and universities have been occupied by students.