A Japanese expert on North Korea says the latest statement by North Korean leader Kim Jong Un's sister is meant to shake the collaboration between Japan, the United States and South Korea.

Kim Yo Jong issued the statement on Thursday. She said a visit to Pyongyang by Japanese Prime Minister Kishida Fumio "might come" if Tokyo "does not lay such a stumbling block as the already settled abduction issue in the future way for mending the bilateral relations."

Nanzan University Professor Hiraiwa Shunji says Japan, the US and South Korea have been solidifying their unity over issues related to the Korean Peninsula since their trilateral summit last year.

He says ties between Seoul and Pyongyang remain very tense as North Korea now appears unwilling to explore peaceful unification with its southern neighbor.

Hiraiwa says North Korea is attempting to rattle the cooperation between Japan, the US and South Korea by implying its readiness to move closer to Tokyo, which wants to resolve the long-standing abduction issue.

He also says Pyongyang wants to make the statement appear to be a message from near the center of power as it took the rare form of one issued by Kim Jong Un's sister towards Japan.

The statement restates North Korea's conventional position that the abduction issue has been settled.

Hiraiwa says Japan will first have to make North Korea change the stance even though Pyongyang seems unwilling to concede it in the interest of better ties.