A wooden boat containing a male corpse was found Saturday in the Sea of Japan off the coast of Sado Island, Niigata Prefecture, the coast guard reported.

The deceased was wearing boots with Korean characters, causing the 9th Regional Coast Guard Headquarters in Niigata to believe that the 8.5-meter vessel drifted toward Sado from North Korea, officials said.

The corpse appears to be that of an adult and, judging by its state of decomposition, had been floating in water inside the boat for a considerable length of time, according to the coast guard's Niigata headquarters.

On Wednesday, another wooden vessel carrying the decomposing bodies of five men also ran aground on Sado Island. The coast guard suspects it was probably a North Korean fishing boat rather a vessel used for espionage.