Turkey has been detaining, abusing and deporting refugees in violation of international law, according to an investigation by Amnesty International.

In a new report, Europe’s Gatekeepers, the rights group says that Turkish authorities have rounded up possibly hundreds of people onto buses and moved them more than 1,000km to detention centres, where they have been held in isolation and often subjected to abusive treatment or been shackled for days on end.

Some also reported being forcibly sent back to their countries of origin, from which they fled.

The research - carried out in Ankara, Bursa, Gaziantep, Hatay, Istanbul, Osmaniye and Sanliurfa - drew on evidence from Afghans, Kurds, Iranians and Syrians.

One 40-year old Syrian man said he had been confined to a room in Erzurum Removal Centre for seven days with his feet and hands bound.

“When they put a chain over your hands and legs, you feel like a slave, like you are not a human being,” he said.

He added that the equipment used on him had tags showing it came from EU funding.

The report said that inmates of the Duzici camp in Osmaniye had been coerced into “voluntary” repatriation.

One 23-year-old woman in the camp was reportedly told by the camp guards that she could “go back to Syria or stay in jail; these are your options”.

Another woman from Idlib in northern Syria said she was held in Duzici with her four children, told to sign a voluntary return agreement written in Turkish, and was refused a translation.

John Dalhuisen, Amnesty's director for Europe and Central Asia, said such treatment was "not only unconscionable... it’s also in direct breach of international law".

He also criticised the EU, who in November promised 3.2 billion euros to Turkey to help improve conditions for Turkey-based refugees and slow the flow of refugees to Western Europe.

“By engaging Turkey as a gatekeeper for Europe in the refugee crisis, the EU is in danger of ignoring and now encouraging serious human rights violations,” Dalhuisen said.

“EU-Turkey migration-related cooperation should cease until such violations are investigated and ended.”

The Turkish government denied Amnesty’s accusations.

“We categorically deny that any Syrian refugees were forced to return to Syria,” a senior Turkish government official told Middle East Eye. “All returnees are independently interviewed by UNHCR staff.”

“Turkey does not tell Syrian refugees where to live. While the majority of Syrians choose to live in urban areas across Turkey, close to 280,000 refugees reside in government-run housing facilities. To prevent social problems, homeless individuals are settled in refugee camps – which they are free to leave.”

He said the refugees held in Duzici refugee camp had “documented ties to criminal gangs” and said their movements were restricted for this reason.

Turkey has been praised in the past for its treatment of refugees fleeing Syria, which now numbers as many as 2.3 million and government officials from the country have expressed their frustration at the EU's foot-dragging over the issue

A proposal from the EU on Tuesday to take Syrian refugees directly out of Turkey said it would set no minimum limit on the number of refugees it was willing to take. However the numbers being discussed are modest.

"If we manage to resettle 10,000 refugees from Turkey by the summer that would be a huge success," a senior official involved with the preparation of the plan told Reuters.