Two Greek men on the island of Rhodes have been arrested on suspicion of spying against Greece, police said late on Saturday.
It did not specify on whose behalf the suspects were allegedly spying.
One of the suspects worked at a consulate on the island, police said in a statement, while the other was employed on a passenger ferry which services a route between Rhodes and the island of Kastellorizo, police said in a statement.
Both islands lie close to the Turkish coast.
A senior police official said that one of the suspects was accused of photographing movements of Greek armed forces in the Aegean Sea.
The suspects were arrested but are not in custody pending investigation, as is the norm in Greece.
Greece and Turkey have a long-standing dispute over explorations rights in the Mediterranean Sea, which is considered to be rich in energy resources.
Tensions flared up in August when Ankara sent a seismic explorations ship in waters claimed by Greece.