Amnesty International slammed Greek authorities for the torture, ill-treatment and illegal pushback of migrants and refugees to Turkey.
In a report titled "Greece: Violence, lies, and pushbacks", Amnesty reported that pushbacks, on land and at sea, sometimes involved people apprehended as far as 700 kilometres within Greek territory.
The rights group described 21 incidents that involved around 1,000 people.
Many had been subjected to violence before being transferred back to Turkey, Adriana Tidona, migration researcher for Europe at Amnesty, said in the report.
"Our research shows that violent pushbacks have become the de facto Greek border control policy in the Evros region," said Tidona, referring to the river bordering Turkey.
"It is clear that multiple arms of the Greek authorities are closely coordinating to brutally apprehend and detain people who are seeking safety in Greece, subjecting many to violence, then transferring them to the banks of the Evros river before summarily returning them to Turkey."
In March, the United Nations Refugee Agency (UNHCR) said that Greece's practice of pushing irregular migrants back to Turkey amounts to a¬†clear violation¬†of the 1951 Refugee Convention, the European Convention on Human Rights and European Union law.