Ten bodies were discovered by the Japanese authorities on the Northwest coast of Japan.
The ships that carried the dead bodies for days were coming from North Korea, revealed the Japanese Coast Guard.
The remains of other two dead bodies were discovered during the weekend, on the beaches of an island, near Niigata City, near the remains of a craft which seems to originate from North Korea, according to the local police.
The corpses in advanced decomposition could not be identified, but more clues suggest they were North Korean fishermen.
According to a spokesperson interviewed by AFP, the Coast Guard has found no object, either in the boat or on the shore, which makes it possible to say with certainty these men were indeed North Korean fishermen.
Dozens of North Korean naval fishing boats fail annually on the northwest coasts of Japan, and sometimes their occupants are found alive.
Experts say North Korean fishermen are urged by the Pyongyang regime to venture far into the Japanese Sea, bordered by the Japanese archipelago, the Korean peninsula, and the Russian Far East, after large catches.
They are thus exposed to great risks because their craft is generally old and sub-fabricated.
North Korean natives recovered in Japan often want to return home, while some choose to flee to South Korea.
The tensions in the region have been resurrected for several months after Pyongyang made its sixth nuclear test and more rocket tests, two of which overflown Japan.