Tension broke between anti-authoritarians and Greek police officers on Saturday afternoon, in central Athens.
The incidents started after a protest held by anti-authoritarian groups in solidarity with hunger strike prisoners protesting against type C maximum security prisons in Greece.
About 600 people gathered in Monastiraki to march towards Syntagma Square and then to the Polytechnic School of Athens.
The anti-authoritarian group placed barricades on Patission avenue and set fire to bins. Around 4 p.m. the protesters entered the Polytechnic School, while the barricades on Patission avenue were removed.
Meanwhile, Greek police officers intervened, making three arrests outside the School. A while later the situation diffused, while the anti-authoritarians left the area.