Amnesty International said Wednesday that Turkish authorities have since September been detaining scores of refugees, including from Iraq and Syria, and abusing and pressuring them to return home in breach of international law.

Amnesty International said Wednesday that Turkish authorities have since September been detaining scores of refugees, including from Iraq and Syria, and abusing and pressuring them to return home in breach of international law.

The rights group also warned that the European Union, which in November reached a deal with Turkey to stem the flow of refugees into Europe, was in danger of being complicit in "serious human rights violations".

"We have documented the arbitrary detention of some of the most vulnerable people on Turkish soil," said John Dalhuisen, Amnesty's director for Europe and Central Asia.

"Pressuring refugees and asylum-seekers to return to countries like Syria and Iraq is not only unconscionable, but it's also in direct breach of international law."

Under the EU-Turkey deal, EU leaders pledged three billion euros ($3.2 billion) in aid to help improve the conditions of the at least 2.2 million refugees currently on Turkish soil from the Syrian war.

In exchange, Turkey agreed to try to limit numbers travelling to Europe and tackle human smugglers who profit from their desperate journeys.

Amnesty said the Turkish authorities have been rounding up "potentially hundreds of people" onto buses in western Turkey and moving them to isolated detention centers in the east, where they are often subjected to abuse.

Most said they had been attempting or intending to cross into the European Union, Amnesty reported.

A 40-year-old Syrian man, who said he was placed into solitary confinement for seven days at a deportation centre with his hands and feet chained, told Amnesty: "When they put a chain over your hands and legs, you feel like a slave, like you are not a human being."

Amnesty said "the apparent policy shift" contrasted with the favorable approach of the Turkish authorities towards refugees until now.

For its part, Ankara angrily rejected Amnesty's accusations, saying it "categorically denied" that any Syrian refugee in Turkey had been forced to return to their conflict-torn home.

"We categorically deny that any Syrian refugees were forced to return to Syria," a Turkish government official said, adding that all returnees were being independently interviewed by the UN refugee agency.

Turkey is the main launching point for migrants coming to Europe, via EU member Greece.