South Korea and the United States began extended negotiations Monday on renewing their civilian nuclear pact, with Seoul pushing for the right to produce its own nuclear fuel.

The current accord, signed in 1974, had been due to expire in 2014, but was extended in April for two years after failing to make progress on the South's demand to reprocess spent fuel rods.

North Korea vowed Wednesday to tighten its hold on its "priceless" nuclear deterrent, confounding reports that it might be willing to resume multilateral talks on denuclearisation.

A lengthy front-page editorial in the North's ruling party daily Rodong Sinmun said a strong nuclear deterrent was the only guarantee of a "final victory" against the forces of imperialism.

North Korea said Tuesday it would allow South Korean businessmen to visit their plants in a shuttered joint economic zone, but declined Seoul's offer of official working-level talks on the complex.

The Committee for the Peaceful Reunification of Korea (CPRK), which handles ties with the South, said it had approved a trip by Seoul businessmen to the Kaesong complex and would guarantee their safety.

South Korea on Monday brushed off an apparent offer by North Korea to resume nuclear disarmament talks, and chided Pyongyang for a recent personal attack on its president Park Geun-Hye.

"Actions are more important than words," Unification Ministry spokesman Kim Hyung-Seok said of the offer contained in a letter delivered Friday by an envoy of North Korean leader Kim Jong-Un to Chinese President Xi Jinping.

South Korea's press on Saturday expressed skepticism over an apparent offer by North Korea that it was willing to return to six-party nuclear disarmament talks.

North Korean special envoy Choe Ryong-Hae met Chinese President Xi Jinping on Friday and reportedly handed him a letter from leader Kim Jong-Un in a sign Pyongyang may be backing away from confrontation with the international community.

A special envoy from North Korean leader Kim Jong-Un told one of China's top officials Thursday that Pyongyang wants peace and is willing to pursue dialogue with key countries, state media reported.

Envoy Choe Ryong-Hae met Liu Yunshan, a member of the Chinese Communist Party's highest ranking body the Politburo Standing Committee, state television reported on its evening newscast.

Japan is considering direct talks with North Korea, the government said Wednesday, adding momentum to the cause after a top level aide to the prime minister made a surprise trip to Pyongyang.

Bilateral talks are on the table as Tokyo seeks to salve the running sore of abductions of its nationals by North Korean spies in the 1970s and 1980s, an issue that inflames public opinion at home.

North Korea has appointed as its new military chief a hawkish general, widely believed to have directed the 2010 shelling of a South Korean border island, state media confirmed Wednesday.

In a brief dispatch, the Korean Central News Agency (KCNA) referred to Kim Kyok-Sik as chief of the Korean People's Army general staff, a notch higher in the military hierarchy than his previous post of defense minister.

A top North Korean general and confidant of leader Kim Jong-Un met a senior Chinese official in Beijing Wednesday, with relations between the allies strained ahead of a China-U.S. summit.

Choe Ryong-Hae, director of the Korean People's Army politburo, is a "special envoy" of the North's young leader, Pyongyang's official news agency said.

North Korea released 16 Chinese fishermen and their boat Tuesday, Chinese state media said, after reports that armed assailants had taken the sailors hostage fueled strains between the neighbors.

"All the fishermen with the boat are safe on their way back," China's Xinhua news agency said, citing a Chinese embassy official in Pyongyang it said had heard the news from the shipowner.