Japan will demand that North Korea hand over the agents involved in the abduction of several Japanese in the 1970s and 1980s, government sources said Thursday.

The government will also ask that Japanese police be allowed to conduct investigations in North Korea and that the North submit detailed information on the special units Pyongyang claims oversaw the abductions.

Japan will press Pyongyang to respond to the requests at every possible opportunity, including future talks toward normalizing bilateral ties, the sources said.

The government is taking a firm stance on the abductions because it believes North Korea never reprimanded the abductors and probably will not voluntarily disclose any information about them.

The government also expects the information will lead to investigations regarding a Japanese collaborator who, according to Pyongyang, helped North Korea’s agents abduct the Japanese.

North Korea told a Japanese government fact-finding mission to Pyongyang that a Japanese national collaborated with its agents in the abduction of Hitomi Soga from Niigata Prefecture on Aug. 12, 1978. But the North said nothing more about the collaborator.

The fact-finding mission was in Pyongyang for four days through Tuesday.

Pyongyang said a North Korean agent named Chang Bom Rim (phonetic spelling) was executed in connection with the abductions after being found guilty in 1998, and that another agent, Kim Song Chol (phonetic), was sent to prison for 15 years for what the North called “ideological correction.”

North Korea disclosed no further details about the two men’s identities, or about when Chang was executed, saying such information is confidential, Japanese officials said earlier.

Japan will also ask South Korea for information concerning former North Korean agents connected with the abductees.

Pyongyang denied that Yaeko Taguchi, abducted in 1978 and reportedly killed in a car accident in 1986, was the Japanese-language instructor known as Ri Un Hye for confessed North Korean agent Kim Hyon Hui, who was convicted by a South Korean court for planting a bomb aboard a Korean Air jetliner that blew it out of the sky in 1987.

Pyongyang also refused to release information about the involvement of North Korean agent Sin Guang Su in the 1980 abduction of Tadaaki Hara, claiming it will release the information after an appropriate legal arrangement is set up between Japan and North Korea.

A South Korean court ruled in 1985 that Sin abducted Hara, who, North Korean claims, died of illness in 1986.

Pyongyang also denied Japanese claims that Megumi Yokota was seen at a university from 1988 through 1991 and that Shuichi Ichikawa was seen at Kim Il Sung University in 1994 by a former Pyongyang agent, saying the claims were “absolutely groundless.”

The National Police Agency has asked the International Criminal Police Organization (Interpol) to put Sin, 73, on an international wanted list for allegedly violating Japan’s passport law by impersonating Hara to illegally obtain a passport.

Police predict the handover negotiations will be difficult. They say Pyongyang is using the handover talks to try to push Japan to begin normalization talks.