A Seoul-based news organization has claimed that North Korean agents were involved in systematically abducting and killing Japanese fisherman between the 1960s and the 1980s, citing testimony from what it says is a former agent involved in the alleged kidnappings. The testimony suggests the number of Japanese nationals snatched by Pyongyang decades ago may be much larger than the officially recognized figure.

During a seminar that the online news site hosted in Tokyo on Thursday, Daily NK presented written testimony it obtained from a person who claims to have been a former North Korean agent attached to unit 448 in the Reconnaissance Bureau of the Korean People’s Army. The document – read out loud in Japanese from the original Korean by an interpreter – said a group of around 120 North Korean operatives were involved in repeatedly abducting Japanese fishermen between 1962 and 1985.

“I believe the number of those abducted from fishing boats would at least count more than 30, the testimony read, adding that abductees were taken back to North Korea to train spies and were used for their expertise on Japanese seas and coastal geography.

Daily NK, which focuses on North Korean news and is partially staffed by defectors from the North, said the former agent was the same person cited in an article on the topic written earlier this week by Japanese daily the Sankei Shimbun.

Targets were small fishing vessels of around 10-20 metric tons operated by three to five fishermen, the document said. North Korean agents sailing on spy ships would approach such vessels at night and seize control.

“Then agents would tie the fishermen up and interrogate them. Especially brutal was how only one of them – who looked young and fit – would be taken. The rest would be tied to the engine room and sunk along with the vessel, according to the document.

The testimony mentions one such mission in the 1980s when the agent was involved in capturing a boat and abducting a fisherman in waters off Aomori prefecture, northern Japan. The vessel and its remaining four crew members were left to sink, the document said.

The issue of North Korea’s past abductions of Japanese citizens has long been a major diplomatic rift between Tokyo and Pyongyang.

North Korea is suspected of abducting foreigners in the 1970s and 1980s, and has so far admitted to abducting 13 Japanese nationals, returning five along with their family members. It claims the rest are dead, despite persistent suspicions that the regime hasn’t come clean regarding the extent of its abductions.

Tokyo officially recognizes 17 abductees – none of whom were fishermen – including those who have been returned. But the disappearances of numerous other Japanese are believed to be linked to possible abductions by North Korea.

And a majority of the 517 South Koreans officially recognized by Seoul as having been abducted by the North since the end of the Korean War were fishermen, raising suspicion that Pyongyang could also have been actively snatching Japanese at sea.

Daily NK said the former agent’s testimony was conveyed to the Japanese government around a year ago in hopes that it would help solve the abduction issue.

Media reported Keiji Furuya, state minister in charge of the abduction issue, saying Friday that the government would re-examine past maritime accidents that occurred around Japanese seas.

An official at the government’s headquarters for the abduction issue told JRT Thursday that they could not comment on the information they gather.

The testimony by the agent comes as Japan surprised its allies South Korea and the U.S. earlier this month when a close aide to Prime Minister Shinzo Abe made a secretive visit to Pyongyang, where he is believed to have discussed the abduction issue, among other matters.

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