Greek police say a teenage Syrian refugee was lightly injured when shot by an unknown man while trying to illegally return to Turkey, after months earlier he fled Turkey to enter Greece.

The 16-year-old, together with a 21-year-old Iraqi, bought a small inflatable dinghy in which they planned to cross the Evros (Meriç) River, on the northeastern border of Greece with Turkey, near Didymoteicho.

Police say both men were threatened on Thursday by two men in a boat from the Turkish side, who fired at them with a shotgun as they ran away. The incident was announced on Friday.

About 57,000 migrants and other refugees, who entered from Turkey, are stuck in Greece after a series of Balkan border closures frustrated their plans to reach Europe's prosperous heartland. Several are returning to Turkey.