"Turkey is a safe country for asylum seekers from Syria, Afghanistan, Pakistan, Bangladesh and Somalia according to joint decree adopted by the foreign and migration ministries," the Greek migration authorities said in a statement.
"They are not in danger because of their religion, their nationality, their political opinions, or inclusion in a social group, and can seek asylum in Turkey rather than in Greece," it added.
Migration minister Notis Mitarachi was quoted as saying: "It will be a big step towards reducing the illegal flow of migrants" and force Turkey to readmit those who have been refused asylum on Greek islands.
For the past 15 months, Turkey has refused to readmit 1,453 refugees that Greek authorities want to send back.
Turkish president Recep Tayyip Erdogan said in February 2020 that he would let migrants who sought to reach the European Union to pass through Turkey.
Tens of thousands surged towards Greece via the crossing between Kastanies and Pazarkule, on the Turkish side of the border, and clashes broke out there for several days.
In early April, Greece accused Turkey of seeking to "provoke an escalation" in the Aegean with "dangerous" manoeuvres and illegal assistance to migrants.
Between January and April, a little more than 1,000 asylum seekers landed on Greek shores according to the UN refugee agency.
Forty seven per cent of the asylum seekers in Greek island camps are Afghans, 15 per cent are Syrians, and nine per cent are from Somalia, agency data show.