The Council of Europe, which safeguards human rights and the rule of law across the region, has criticized Greece for police violence and poor conditions in its over-crowded prisons, urging Athens to overhaul a system reaching "breaking point".
"Vulnerable prisoners are not being cared for and, in some cases, are being allowed to die," the Council's Committee for the Prevention of Torture and Inhuman or Degrading Treatment or Punishment said in a report based on a 2015 visit to Greece.
"The main problems of overcrowding and chronic shortage of staff persist," it said, acknowledging that Athens had taken steps to reduce the number of inmates, many of whom had to face widespread violence among prisoners and intimidation.
"Further efforts need to be made to promote alternatives to imprisonment and to move away from the current situation whereby prisons in Greece are merely acting as warehouses," it said.
It said that in some wings of Athens' high security prison in Korydallos, there were only one or two custodial officers for 350 to 400 prisoners. It also said unaccompanied minors were placed in unacceptable conditions.
The Greek justice ministry said it was "working intensively" to deal with the issues mentioned in the report and added that the number of prisoners has dropped from roughly 11,500 prisoners in 2014 to 9,500 today.
Rights groups and critics have long accused Greek police of detaining immigrants and other prisoners in shocking conditions.
The committee also condemned the detention of unaccompanied minors for several days or weeks in police stations and called on Athens to provide them with an appropriate shelter.
More than 22,000 migrants are currently in Greece, many of them children.