Two people were injured and 42 detained on Saturday night during disturbances that followed a march by the far-right Chrysi Avgi (Golden Dawn) group.
The rally was held to mark the anniversary of the 1996 Imia crisis, during which three Greek military officers were killed.
Hundreds of nationalists marched from a statue in central Athens erected in honor of the three soldiers toward the US Embassy. The march was heavily policed and there were no disturbances, but after the rally a group of extremists took the metro to Omonia station, where they began to attack immigrants and pull other passengers off trains.
All of the alleged assailants were released Sunday.