At least one person died and seven were injured in clashes between prisoners at Korydallos prison in Athens, on Thursday evening.
According to preliminary reports, the clashes broke out in the psychiatric ward of the prison.
Reports said the victim, whose identity was not immediately made public, died after being stabbed with a knife.
The reason for the brawl, involving ethnic Greeks from the former Soviet Union, Albanian and Georgian inmates, was not known.
The injured were rushed to nearby hospitals for treatment.