Japanese fishermen may have been abducted by North Korea decades ago while operating in the Sea of Japan, a South Korean activist who heads a group of family members whose relatives had been abducted to the North said Tuesday.

Citing a North Korean source, Choe Seong-ryong said North Korea, which was regularly seizing South Korean fishing boats back then, may have sought to use Japanese fishermen as operatives and exploit their familiarity with Japanese coastal areas.

He said he learned from the source that a number of Japanese abductees in North Korea were once fishermen.