Story highlights So-called North Korean ghost ships have washed up in Japan for years

The bodies on-board may belong to attempted refugees, or fishermen blown off course

Tokyo (CNN) At least four ships have washed up on Japan's west coast this month, some with bodies on board, and while authorities haven't confirmed their origin, signs suggest they're from North Korea.

Eight skeletons were found in the hull of one wooden boat that washed ashore on Miyazawa beach in the northwest of Japan's main island Honshu, the Akita Coast Guard said Monday.

The unidentified boat was spotted drifting off shore on Friday but the grim discovery was only made when it reached land.

While officials would not confirm the boat was from North Korea, it matches a spate of vessels and debris that have ended up on Japan's west coast.

Satoru Miyamoto, a professor at Seigakuin University and an expert on North Korea, said the number of ships washing ashore on Japan's coast has risen since 2013.

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