North Korean leader Kim Jong Un's powerful sister said Tuesday Pyongyang would reject "any contact or negotiations" with Japan, just a day after she said Tokyo's Prime Minister Fumio Kishida had requested a summit with her brother.

Relations between the two countries are historically strained, including by a long-running kidnapping dispute and North Korea's banned weapons programmes, but Kishida has recently expressed a desire to improve ties, which Pyongyang has hinted it is not opposed to.

Last year, Kishida said he was willing to meet Kim "without any conditions", saying Tokyo was willing to resolve all issues, including the abduction by North Korean agents of Japanese citizens in the 1970s and 1980s, which remains an emotive issue in Japan.

Kim Yo Jong -- who is one of the regime's key spokespeople -- said on Monday that Kishida had requested a summit with Pyongyang's leader, adding a meeting was unlikely without a policy shift by Tokyo.

But on Tuesday, she said Pyongyang would reject any contact with Japan, citing Tokyo's lack of "courage" for "new" North Korea-Japan relations, including over its stance on the abduction issue and North Korea's military programmes.

North Korea "has clearly understood once again the attitude of Japan and, accordingly, the DPRK side will pay no attention to and reject any contact and negotiations with the Japanese side," Kim Yo Jong said, according to Pyongyang's official Korean Central News Agency.

"The DPRK-Japan summit is not a matter of concern to the DPRK," she added, referring to the North by its official name.

Kishida said Tuesday that he was aware of media reports on Kim Yo Jong's comments, but would "refrain from commenting on each of these remarks."

"Japan will continue to make efforts to resolve the various issues with North Korea in accordance with our existing policy," he said.

  Abductions 

 North Korea admitted in 2002 that it had sent agents to kidnap 13 Japanese people in the 1970s and 1980s who were used to train spies in Japanese language and customs.

The abductions remain a potent and emotional issue in Japan and suspicions persist that many more were abducted than have been officially recognised.

Japan's Chief Cabinet Secretary Yoshimasa Hayashi told reporters Monday that North Korea's "claim that the abduction issue has already been resolved is totally unacceptable".

In response, Kim Yo Jong said this showed "Japan has no courage to change history, promote regional peace and stability and take the first step for the fresh DPRK-Japan relations."

"This is proved by the attitude of Japan clinging to the unattainable issues which can never be settled and have nothing to be settled," she added.

Analysts said North Korea's abrupt reversal could be a negotiating ploy designed to "enhance leverage" in any future talks.

"North Korea is attempting to explore economic avenues by improving relations with Japan," Ahn Chan-il, a defector-turned-researcher who runs the World Institute for North Korea Studies, told AFP.

But Kim Yo Jong slammed Kishida's entire outreach as "politically-motivated" and said Pyongyang would no longer engage.

"It was the Japanese side that knocked at the door first requesting 'the Japan-DPRK summit without preconditions', and the DPRK only clarified its stand that it would welcome Japan if it is ready to make a new start, not being obsessed by the past," she added.