Thousands of protesters demonstrated in Athens, Thessaloniki and other Greek cities on Tuesday against police violence, a day after a Roma youth was shot in the head in a police pursuit.
The demonstrations were part of planned annual commemorations to mark the 2008 death of Alexandros Grigoropoulos, a 15-year-old fatally shot by police.
His death shocked the nation and sparked days of youth riots in major cities at the time.
Police estimated more than 11,000 protesters turned out across the country on Tuesday.
Around 4,000 police were deployed in Athens with tensions running high after Monday's shooting.
A police motorcyclist in Greece's second city Thessaloniki early on Monday shot a 16-year-old Roma boy after he drove away from a petrol station without paying.
The teenager was hospitalised and in a critical condition, according to media reports.
Some of the most violent protests Tuesday were in Thessaloniki, where police fired tear gas after protesters set fire to rubbish bins and threw rocks and Molotov cocktails at riot police.
Some 6,500 rallied in Athens where a banner referenced the unpaid 20-euro ($21) petrol bill, saying "A life is worth 20 euros".
A police officer has been arrested and charged with attempted manslaughter over the incident.
The Greek police department said the youth had tried to ram officers in pursuit on motorbikes in his attempt to evade arrest.
A group of Roma on Tuesday threw objects at riot police outside the courts in Thessaloniki where police said about 5,000 people joined the demonstration.
In Athens, another group set fire to bins on a major highway.
There are frequent claims that police in Greece are poorly trained.
A senior police unionist on Tuesday told state TV ERT that the officer who shot the Roma teen is a 14-year veteran.
On Monday evening, Roma protesters set roadblocks ablaze, threw Molotov cocktails at riot police and smashed shop windows in the centre of Thessaloniki.
Another Roma youth was killed in 2021 near the port of Piraeus, also in a police pursuit.