Clashes broke out between Greek police and self-styled anarchists in a central Athens neighbourhood early Sunday.
The left-wing activists lit trash cans on fire and hurled stones and Molotov cocktails at police, television images showed.
The neighbourhood had become quiet by Sunday morning.
The violence occurred near the Athens Polytechnic university in the city's Exarchia district, which sees regular outbreaks of riots and is considered a hotbed of anarchism. The district has also attracted gangs of drug dealers.
Anarchists have recently taken to stopping public buses, removing the drivers and passengers, and then lighting the vehicles on fire.