A Merchant Marine Ministry statement said the vessel, which is not in any danger, was spotted 60 miles offshore today.
Greece and Italy are major entry points for African and Asian migrants seeking a better life in Europe.
In the past two weeks, about 400 people have died trying to reach the Italian island of Lampedusa on rickety smuggling ships.
The Greek ministry said a merchant ship, escorted by a coast guard patrol boat, was towing the vessel to the southern port of Pylos on the Mediterranean.