Greece faces a "humanitarian crisis" over its mistreatment of asylum-seekers and migrants, according to a report by Amnesty International.
The group accuses the government of detaining thousands of refugees, including many children, in "shameful [and] appalling" conditions.
Greece is a major gateway for migrants from Asian and African countries as they try to enter the European Union.
Attacks against foreigners have been on the rise in the debt-stricken nation.
The report claimed that Greece systematically fails to provide the most basic requirements of safety and shelter to the thousands of asylum-seekers passing through the country ever year.
"Greece is clearly failing very significantly to absorb and respect the rights of the many migrants that are crossing its land and sea borders with Turkey," Amnesty International spokesman John Dalhuisen said.
"It wouldn't be an exaggeration to say that the EU has a humanitarian crisis not beyond its borders, not on its borders, but within its borders."
'At mercy of violence'
In particular, the report highlights the plight of unaccompanied children held in "very poor conditions" at the recently opened Corinth detention centre, calling it a breach of international standards.
The study also draws attention to the "dramatic increase" of racially motivated attacks, now reported on an almost daily basis.
Mr Dalhuisen said many migrants found themselves "at the mercy of violence" in the capital, Athens.
The BBC's Mark Lowen in Athens says there is growing pressure on Greece to develop an effective and fair asylum system and improve its policy towards migrants, and on Europe to step in with concrete solutions.
The far-right Golden Dawn party has recently seen a rise in its popularity and won 18 seats in parliament on a wave of public anger against austerity.
The party blames some of the country's economic problems on illegal immigration.
Observers see this as a key factor contributing to the growing climate of xenophobia in Greece.
In August, police in Athens arrested more than 1,100 immigrants without documents, and brought in another 4,900 for questioning as part of Operation Xenios Zeus.