Violence breaks out in the Exarchia district of the Greek capital, where 15-year-old Alexis Grigoropoulos was shot dead on December 6, 2008.
Greek police clashed with protesters on Thursday after demonstrations to mark the 10th anniversary of the killing of a teenage boy by police, which triggered the country's worst riots in decades.
Hundreds marched peacefully through central Athens in a tribute to 15-year old Alexandros Grigoropoulos who was shot dead in 2008.
After the evening march, police fired tear gas to disperse protesters hurling petrol bombs at them in the bohemian Exarchia district, where the unarmed boy was killed.
Some of the protesters set garbage containers on fire and set cars alight.
Earlier, people laid flowers and lit candles during a memorial service on the spot where Grigoropoulos was killed.
Police had deployed more than 2,000 officers in Athens.
Some in full riot gear formed protective cordons outside parliament and hotels in the city, while a helicopter hovered over the central Syntagma Square and neighbouring districts through the day.
Around noon, hundreds of students marched towards parliament.
Clashes also broke out during demonstrations in the northern city of Thessaloniki, with police firing tear gas and stun grenades at protesters hurling stones and petrol bombs at them.
On the night of December 6, 2008, hours after Grigoropoulos was shot, thousands took to the streets of Athens, torching cars and smashing window shops and looting.
The riots, which were also fuelled by anger over unemployment and economic hardship in a prelude to Greece's debt crisis, lasted for weeks.