Four women and a child have died after their boat capsized off the Greek island of Samos.
They are thought to be the first deaths in the area since a new deal with Turkey went into force on Monday with the aim of deterring migrants. Five other people were saved and a search is underway for four more.
This week, dozens of migrants were returned to Turkey under the new deal with the EU, which has been criticized by human rights groups, BBC reported.
Survivors from the latest drowning told officials that they were travelling on a 3.5-meter vessel made of plastic.
On Friday, two ferries carrying more than 120 people, mostly Pakistanis, arrived in western Turkey from the Greek island of Lesbos.
More than 200 people were sent back on Monday, but returns have been stalled by a surge of asylum applications in Greece.
The EU-Turkey deal aims to ease the uncontrolled mass movement of people into Europe.
Under the new agreement, migrants who have arrived illegally in Greece since 20 March are expected to be sent back to Turkey if they do not apply for asylum or if their claim is rejected.
For each Syrian migrant returned to Turkey, the EU is due to take in another Syrian who has made a legitimate request.
Human rights organizations have attacked the scheme as badly flawed, warning that Turkey is not a safe place to return people.
Amnesty International reported that there was just one official who was processing applications on the island of Chios, and out of 833 claims that had been filed, he had processed only 10.
