It said five others were missing and a search was underway.
The coast guard said it had plucked three people from the sea with the help of local fishing boats after the vessel with the refugees aboard went down off the coast of the western province of Izmir. Two other people swam to shore, it added.
One Iranian and 14 Afghan nationals were on the boat before it sank, the coast guard said, adding that search operations for the five missing people were continuing.