Migrant returns from Greece to Turkey will begin on Monday, April 4, under the terms of an EU deal that has worried aid groups, as Athens struggles to manage the overload of desperate people on its soil, AFP reports.

Turkish Prime Minister Ahmet Davutoglu on Thursday confirmed the start of the returns in one of his regular televised addresses to Turks.

Under the scheme agreed with the EU, one Syrian refugee will be settled in Europe legally in return for every migrant taken back by Turkey from Greece.

"That's to say, with the one-for-one method, the number of refugees in Turkey will not increase," he said, according to AFP. "This practice will begin as of April 4."

Although many of the details remained unclear, a European Commission source told AFP there was "a major engagement on the part of Greece and Turkey towards sending 500 people back on April 4, barring a last-minute problem."

Those being returned would include "Syrians who have not requested asylum, Afghans and Pakistanis," the official said, confirming it would be the first batch sent back under a deal reached between Brussels and Ankara on March 18.

EU spokeswoman Natasha Bertaud confirmed that Monday was the "target day" when those whose asylum claims had "been declared inadmissible" would be returned to Turkey.

At the same time, the EU would start resettling Syrian refugees living in camps in Turkey, she said.