Greece says it has returned 12 Syrians, including a woman and her four children, to Turkey as part of a European Union-Turkey agreement aiming to stop the flow of refugees and migrants across the Aegean to Europe's more prosperous heartland.

The 12 were flown from the Greek island of Lesbos to Adana in Turkey Wednesday by a plane chartered by the European border agency Frontex, Greece's citizens' protection ministry said, noting all had expressed the wish to return and none had applied for asylum in Greece.

Under last month's EU-Turkey deal, people arriving clandestinely on Greek islands from Turkey from March 20 onwards face being returned unless they successfully apply for asylum in Greece. So far, 386 people have been returned under the deal, Greece says.