At least 12 people believed to be Syrian refugees drowned as two boats sank after leaving southwest Turkey for the Greek island of Kos on Wednesday, a senior Turkish naval official said.
The two boats, carrying a total of 23 people, had set off separately from the Akyarlar area of the Bodrum peninsula.
The confirmed dead included five children and one woman. Seven people were rescued and two reached the shore in lifejackets. The official said hopes were fading of saving the two people still missing.
Television images showed the lifeless body of a small boy dressed in a red t-shirt and blue shorts lying face-down on the sand in Bodrum, one of Turkey's most popular beach resorts.
Tens of thousands of Syrians fleeing the war in their homeland have descended on Turkey's Aegean coast this summer to board boats to Greece, their gateway to the European Union.
The official said almost 100 people in all had been rescued by Turkish vessels overnight as they tried to reach Kos.
Aid agencies estimate that, over the past month, about 2,000 people a day have been making the short crossing to Greece's eastern islands on rubber dinghies.
A ship bringing about 1,800 migrants and refugees from one of the islands arrived at the port of Piraeus near Athens on Tuesday night, the Greek coastguard said.
Thousands of people, mainly Africans, have also been trying to reach Europe via boat from Libya to Italy. The United Nations refugee agency UNHCR said four bodies had been pulled from the central Mediterranean on Tuesday and 781 migrants rescued, mostly from Nigeria, Ivory Coast and Senegal.