A march through central Athens to mark the sixth anniversary of the fatal police shooting of an unarmed teenager quickly turned violent Saturday, as marchers damaged store fronts and bus stations and set fire to clothes looted from a shop.

Clashes also broke out between police and demonstrators marching through Thessaloniki. At night, police fired tear gas and stun grenades after a crowd of marchers beat up two plainclothes police officers. No casualties were reported in either city.

The marches are commemorating the Dec. 6, 2008, police killing of 15-year-old Alexandros Grigoropoulos in the capital, which led to two weeks of the most violent rioting Greece had seen in decades.

The marches come at a time when nearly nightly violent protests are being held by supporters of one of Grigoropoulos' friends, jailed anarchist and convicted bank robber Nikos Romanos, 21. - AP