Protesters fought riot police in Athens on Thursday as there were gatherings to remember the death of Alexis Grigoropoulos ten years ago.
Hooded youths smashed bus shelters and threw rocks and Molotov cocktails soon after a march began in the Greek capital. Police responded with tear gas.
There were similar incidents in the northern city of Thessaloniki and the rallies continued into the night.
Some 2,500 police and a helicopter were deployed. At least 28 people were detained.
The teenager's killing on December 6, 2008 sparked major riots that spread from Athens across the country, lasting for weeks.
The 15-year-old died after he was shot by a policeman. Grigoropoulos had been on a night out with friends in Athens' Exarcheia district at the time.
The policeman, who claimed he had fired into the air when youths attacked him, was sentenced to life in prison. A second policeman present at the shooting was sentenced to 10 years, but was granted a conditional release several years ago.
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There was gathering on Thursday night and people laid flowers and lit candles at the place where Grigoropoulos died.
Since 2009, annual marches marking the anniversary have often turned violent. Although the unrest was originally triggered by Grigoropoulos' death, its continuation has been linked with frustration among young people over austerity and high youth unemployment in Greece since then.
rc/amp (dpa, AP)