Twenty-one migrants including five children drowned after a boat capsized off the Turkish coast, local officials said on Friday.
The victims' nationalities were not yet known. Officials said two people were rescued by the Turkish coastguard and another two managed to make it out of the water on their own.
The boat capsized off Turkey's largest island, called Gokceada or Imbros, which is located in the Aegean Sea off the coast of the northwestern province of Canakkale near Greece's Lemnos island.
"Security teams found the bodies of 21 people including five children," the local governor's office said in a statement.
The search and rescue operation was backed by one aeroplane, two helicopters, one drone, 18 boats and 502 personnel, it added.
Turkey is hosting nearly four million refugees, mostly Syrians.
Many migrants try to reach the Greek islands from Turkey's western coasts in order to head to prosperous European Union countries, with many dying in the perilous sea crossing.
Local officials said that the boat began sinking overnight and on Friday many ambulances were standing by at the port of Kabatepe near Gokceada.
There has been heightened migrant activity in waters between Turkey and Greece in recent weeks.
The Turkish coastguard indicated that it had rescued or intercepted several hundred migrants, including children, attempting to cross to Greece since the start of the week.
The Mediterranean Sea has for several years been the centre of migrant flows from Africa and the Middle East to Europe.
An acute migrant crisis peaked in 2015 as migrants, many fleeing the Syrian civil war, sought refuge in Europe.
Turkey struck a deal with the European Union in 2016 to curb the influx of refugees trying to reach the EU in return for financial assistance and other incentives.
The issue of illegal migrants is a thorn in relations between NATO members Turkey and Greece, who are already embroiled in long-standing disputes from exploratory drilling rights in the eastern Mediterranean to the divided island of Cyprus and rival claims over the Aegean Sea.
Greece also frequently accuses Turkey of waving through migrants from across their joint border and at sea.
Ankara in turn accuses Athens of illegal pushbacks of migrant boats.
Turkey and Greece agreed in December, when Turkish President Recep Tayyip Erdogan visited Athens, to open a new page in their troubled relations and address their problems including irregular migration through dialogue and mutual goodwill.
The issue of migrants is likely to figure highly in talks when Greek Prime Minister Kyriakos Mitsotakis visits Ankara in May.
