"We condemn such cruel and degrading treatment and call for a full investigation into this incident," the UNHCR said in a tweet.

EU border agency Frontex confirmed to AFP the arrival of the group in circumstances that the Greek Ministry for Civil Protection said sent out an "inhuman image".

"The Frontex officers reported that the migrants were found almost naked and some of them with visible injuries," said Paulina Bakula, spokeswoman for the organization.

Bakula, speaking from Frontex's Warsaw HQ, said Frontex officers worked with Greek authorities to provide the migrants — mainly Afghans and Syrians — with immediate assistance.

She added the organization had informed the agency's fundamental rights officer of a potential rights violation.

Greek Minister for Civil Protection Takis Theodorikakos accused Turkey of "instrumentalizing illegal immigration" in the latest of a series of recriminations on migration between the neighbors.

Theodorikakos told Skai television many of the migrants had told Frontex that "three Turkish army vehicles had transferred them" to the river, which acts as a natural border.

Ankara denied any responsibility, and Interior Minister Ismail Catakli called on Greece to stop what, in a tweet, he termed its "manipulations and dishonesty".

Fahrettin Altun, the communications director of Turkey’s president, accused Greek Migration Minister Notis Mitarachi of “sharing false information” after the official tweeted a photo of the naked migrants on Saturday and blamed Turkey.

Altun tweeted in Turkish, Greek and English that this was to “cast suspicion on our country,” while calling on Athens to abandon its “harsh treatment of refugees.”

“Greece has shown once again to the entire world that it does not respect the dignity of refugees by posting these oppressed people’s pictures it has deported after extorting their personal possessions,” he said.

On Saturday, Mitarachi described the incident as a "shame on civilization".

Athens regularly denies accusations from NGOs and media as having, on many occasions, sought illegally to push migrants back to Turkey, sometimes using force.

Last month, Turkish President Recep Tayyip Erdogan used a UN address to accuse Greece of transforming the Aegean Sea into a "cemetery" with "oppressive policies" on immigration.