Pyongyang said on Friday it had "nothing to talk" about with Japan after claiming that a Japanese diplomat in China had made contact with a North Korean counterpart.

Relations between the two East Asian neighbours have long been strained over the kidnapping of Japanese people in the 1970s and 1980s and North Korea's banned weapons programmes, although there had been tentative recent signs of a thaw.

A North Korean diplomat in China  said on Friday an official from the Japanese embassy in Beijing had proposed "contact through an e-mail" to a councillor at its embassy in the Chinese capital but the proposal was rejected by foreign minister Choe Son Hui.

"... the DPRK will not allow any attempt of Japan to contact the former,"  Choe said, using the acronym for North Korea's official name.

"The DPRK-Japan dialogue is not a matter of concern to the DPRK."

Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, had said on Monday that Japanese Prime Minister Fumio Kishida had requested a summit with her brother, although a meeting was unlikely without a policy shift by Tokyo.

But the next day she said Pyongyang would reject any such contact, citing Japan's lack of "courage" to rebuild North Korea-Japan relations.

In a separate statement on Friday, North Korea's ambassador to China Ri Ryong Nam said: "We have nothing to talk with the Japanese side."

"I make it clear once again that the DPRK has no reason to meet with the Japanese side at any level," Ri said.

Kishida said last year he was willing to meet Kim Jong Un "without any conditions" and address all matters, including the abduction of a dozen Japanese citizens by North Korean agents.

Despite Kim Yo Jong's earlier comments, Kishida said on Thursday he was still willing to work towards a summit to secure the return of the abducted Japanese and address other subjects.

"I'd like to continue to hold high-level dialogues (with North Korea) under my direct supervision," he told reporters.

However, Choe criticised Kishida on Friday for referring to the abductions, saying she "cannot understand why he persistently adheres to the issue".