Self-styled anarchists on Monday clashed with supporters of the neonazi Golden Dawn near the Athens Appeals Court where the trial of members of GD is underway.
Around 20 people threw stones and beams of wood at the GD supporters as they were arriving at the court house.
A riot police unit intervened and two people were arrested.
Meanwhile other anarchists climbed onto the rooftops of nearby buildings and continued to throw stones at GD supporters.
There were no reports of any injuries.