Conditions in Greece for people held in detention are "sub-standard", according to the preliminary findings of the United Nations Working Group on Arbitrary Detention announced on Thursday in Athens.
"While domestic legislation provides for proper conditions for those who are in detention, we found that in real life the conditions of those who are in detention facilities are far below the international human rights standards and below the standards set up by international law," said human rights expert Vladimir Tochilovsky.
Tochilovsky, who completed an 11-day visit to various facilities around Greece together with another of the group's experts, Mads Andenas, particularly noted the overcrowded conditions in detention facilities.
According to the expert, people are often detained for months in small cells in police stations designed to hold people for only 24 hours, "without the proper conditions and without access to legal assistance".
"The fact is that most of [those waiting for trial] did not have the free legal assistance [they are entitled to] in the pre-trial stage," he said.
Tochilovsky noted that migrants and asylum-seekers could even be detained for as long as 18 months.
"If we take into account the sub-standard conditions where they are detained... it amounts to criminal punishment for people who have committed no crime," he said.
"We also found an alarming situation regarding unaccompanied minors in detention," he added.
There were also references to instances of arbitrary detention concerning members of the local Roma community, during recent sweep operations carried out by the police.
"They are citizens of Greece, but were singled out because of their ethnicity," Tochilovsky said.
"We've been told on several occasions about brutality and physical abuse [by the police]," he added.
The group will write a draft report and send it to the Greek government for comments and observations, before producing its final report.
Due to its geographical location, Greece serves as the main entry point for migrants from Asia and Africa crossing illegally into the European Union.
In a country experiencing a sixth year of continuous recession, a crippling economic crisis and harsh austerity measures, international human rights organisations have voiced concern over a rise in social tensions and racist attacks.
In November, the US embassy in Athens warned Americans to be wary of attacks targeting perceived foreign migrants.
In a Greek first, neo-Nazi party Golden Dawn saw 18 deputies elected to the country's 300-seat parliament last year.