Nuclear-armed North Korea has started operating a new plant inside its uranium enrichment complex, boosting its capacity to generate fuel that could be used to make atomic weapons, a report said Wednesday.

"Infrared cameras used by South Korean and U.S. intelligence authorities have detected heat that was emitted when gas centrifuges in the new plant began operating," the Joongang Ilbo daily quoted an unnamed official in charge of handling North Korean intelligence. 

North Korea's top newspaper carried pictures Wednesday of leader Kim Jong-Un walking without a stick, apparently showing he has recovered from either an injury or surgery to his leg.

Rodong Sinmun, the official daily of the state's ruling Korean Workers Party, carried a photo of a smiling Kim walking without the cane he was seen using last month.

North Korea on Tuesday ruled out any dialogue with the United States about its nuclear program and human rights record, saying the U.S. was trying to destroy its system.

The North "will never allow any human rights dialogue or nuclear one with the enemy keen to overthrow it", a foreign ministry spokesman said through the official Korean Central News Agency.

Japan's Prime Minister Shinzo Abe said Thursday that North Korea had told a delegation from Tokyo it would "deepen" an investigation into the Cold War kidnapping of Japanese citizens, according to a report.

"The North Korean side showed a policy to Japan that it will deepen (its) investigation from a new angle regardless of past investigations' results," Kyodo news agency quoted Abe as saying.

North Korea warned Thursday it would stop engaging with the international community on human rights issues if a resolution is presented to the United Nations requesting Pyongyang be referred to the International Criminal Court for possible prosecution.

A draft resolution is to be presented by the EU and Japan to the U.N. General Assembly later this week that is expected to harshly condemn rights abuses in North Korea, based on the findings of a recent U.N. report.

A top U.N. rights investigator said Tuesday it was time for the global community to challenge North Korea on a whole "new level" by pursuing war crimes charges against Pyongyang, despite the regime's recent efforts to engage on the rights issue.

Marzuki Darusman, the U.N. special rapporteur on North Korea, urged the General Assembly to refer a damning report by a U.N.-mandated Commission of Inquiry, detailing systemic rights abuses in the nuclear-armed nation, to the International Criminal Court (ICC) for possible prosecution.

North Korea has built a test facility that may be intended to develop a marine-based ballistic missile launch capability, using submarines or surface vessels, a U.S. think-tank said Tuesday.

While submarines carrying ballistic missiles could provide the North Korea with a survivable second-strike nuclear capability, the U.S.-Korea Institute at Johns Hopkins University stressed that Pyongyang was likely "years" from achieving the required technology.

South Korea sent a new message Tuesday prodding North Korea to confirm if it would take part in the proposed resumption of high-level talks, criticizing the reclusive nation's "ambiguous attitude".

The two Koreas agreed earlier this month to restart the dialogue, and South Korea had proposed meeting on October 30.

South Korea's spy agency believes North Korean leader Kim Jong-Un, who recently dropped out of public view for nearly six weeks, had surgery to remove a cyst from his ankle, Yonhap news agency reported Tuesday.

In a briefing for legislators, the National Intelligence Service (NIS) said it also had information that Kim had demoted around 200 military officers and that 50 executions had been carried out in the North so far this year.

North Korea's ambassador on Monday met with the U.N. rights investigator for talks on a possible invitation amid a U.N. push for the Pyongyang regime to face war crimes prosecution.

North Korean counsellor Kim Song told Agence France Presse that the meeting with special rapporteur Marzuki Darusman was to discuss "our future cooperation in the area of human rights."