Four migrants have been found dead on a crippled boat 15 miles east of the island of Thassos

Four people believed to be migrants have been found dead on a crippled boat in the northern Aegean Sea and 15 survivors have been rescued, Greek authorities said Wednesday.

The boat was located following a 17-hour search and rescue operation by sea and air, after somebody believed to be a passenger on the inflatable dinghy made a distress call to Greek officials late Tuesday.

All the passengers on the boat were men, but their nationalities or point of departure weren’t immediately known, the Merchant Marine Ministry said.

The ministry couldn’t provide any information on how the victims died or how many people had been on the boat when it started its journey – most likely from the Turkish coast.

A coast guard vessel found the boat east of the island of Thassos, and the ministry initially said three of its passengers were unconscious. When the migrants were taken to the northern port town of Kavala later Wednesday, doctors pronounced them dead, together with a fourth man.