Amnesty International has accused European leaders of “double speak” over a deal which will see Europe-bound migrants returned to Turkey.

The leading human rights charity said the deal failed to hide the EU’s “dogged determination to turn its back on a global refugee crisis”. Under the plan, migrants arriving in Greece will be sent back to Turkey if their asylum claim is rejected.

In return, Turkey will receive aid and political concessions. John Dalhuisen, Amnesty International’s Director for Europe and Central Asia, said promises by the EU to respect international and European law “appear suspiciously like sugar-coating the cyanide pill that refugee protection in Europe has just been forced to swallow”. He added: “Guarantees to scrupulously respect international law are incompatible with the touted return to Turkey of all irregular migrants arriving on the Greek islands as of Sunday.

Turkey is “not a safe country for refugees and migrants”, Dalhuisen said, adding that any deal to return migrants based on claims it was would be “flawed, illegal and immoral”. It is hoped the plan, agreed at a summit in Brussels, will deter people from taking the often dangerous sea crossing from Turkey to Greece, reports the BBC. As part of the arrangement, EU countries will resettle Syrian migrants already living in Turkey. EU leaders have welcomed the agreement, but German Chancellor Angela Merkel warned of legal challenges to come.

Some of the initial concessions offered to Turkey have been watered down and some EU members expressed disquiet over Turkey’s human rights record. Turkish Prime Minister Ahmet Davutoglu hailed it as a “historic” day.

European Council President Donald Tusk said there had been unanimous agreement between Turkey and the 28 EU members. The UN warned that Greece’s capacity to assess asylum claims needed to be strengthened for the deal. Implementation was “crucial”, the organisation said.

An EU source told the BBC up to 72,000 Syrian migrants living in Turkey would be settled in the EU under the agreement. They added that the mechanism would be abandoned if the numbers returned to Turkey exceeded that figure. Since January 2015, a million migrants and refugees have entered the EU by boat from Turkey to Greece. More than 132,000 have arrived this year alone. Tens of thousands are now stuck in Greece as their route north has been blocked.

Greek Interior Minister Panagiotis Kouroublis has compared conditions at the Idomeni camp, on the border with Macedonia, to a Nazi concentration camp.