ATHENS (AP) — Clashes broke out in Athens and the port city of Patras late Friday, leaving at least two people injured, following protests held to mark the anniversary of the fatal police shooting of a teenager that sparked major riots 11 years ago.

In Athens, scores of youths set fire to trash bins and used hammers to smash paving stones and hurl the fragments at riot police. At least 15 people were detained.

Authorities said two people were hurt, while at least two suspected rioters were arrested and another 20 were detained in Patras, 210 kilometers (130 miles) west of Athens, where youths threw petrol bombs at police and more extensive clashes occurred.

Police said about 5,000 people, including youths from anarchist and anti-establishment organizations, took part in an evening demonstration in Athens, where earlier some 2,000 attended a midday rally organized by student groups.

About 3,500 police officers took up positions around the Greek capital in an attempt to prevent violence that has marred similar commemorations in previous years. Authorities shut down main roads in the city center and closed at least one subway station.

Protest marches were also held Friday in Greece’s second-largest city Thessaloniki and elsewhere to commemorate the death of 15-year-old Alexandros Grigoropoulos, who was shot dead by a policeman during a street altercation in central Athens on Dec. 6, 2008. The riots that ensued in Athens and other cities lasted for about two weeks and were the most severe the country had seen in decades.

The officer convicted and jailed for the killing was released earlier this year after his sentence was reduced on appeal.

Riot police detains a protester during minor clashes in Athens, Friday, Dec. 6, 2019. (AP Photo/Yorgos Karahalis)

Riot police use tear gas against hooded protesters during minor clashes in Athens, Friday, Dec. 6, 2019. Thousands of protesters in Greece have joined marches in the nation’s capital and other cities to mark the anniversary of the fatal police shooting of a teenager that sparked extensive rioting 11 years ago. (AP Photo/Yorgos Karahalis)

FILE- Riot police detains a man during minor clashes in Athens, Friday, Dec. 6, 2019. Thousands of protesters in Greece have joined marches in the nation’s capital and other cities to mark the anniversary of the fatal police shooting of a teenager that sparked extensive rioting 11 years ago. (AP Photo/Yorgos Karahalis)