South Korea's top nuclear envoy met with his Chinese counterpart on Wednesday and discussed North Korea's nuclear weapons program, after a U.N. nuclear watchdog cited major progress in the construction of a light water atomic reactor in the North.

Lim Sung-nam, Seoul's chief negotiator to six-party talks aimed at ending the North's nuclear ambitions, had talks with Wu Dawei during his two-day trip to Beijing.

"The two diplomats exchanged opinions about the situation on the Korean Peninsula and discussed ways to strengthen further bilateral cooperation," said an official from the South Korean embassy in Beijing, asking not to be named.

"The two sides agreed that the six-nation talks are necessary to solve the North Korean nuclear issue and they will closely collaborate to build peace and stability on the Korean Peninsula."

The official added that Lim will have meetings with other Chinese officials and scholars.

Speaking before departure for Beijing, Lim told Yonhap News Agency by telephone he "will jointly assess the current situation on the Korean Peninsula with the Chinese side."

The two sides will also hold consultations on "how to cope with North Korea's nuclear issue and how to maintain the situation on the Korean Peninsula," Lim said.

The six-party talks, which involve the two Koreas, the United States, China, Russia and Japan, have been dormant since late 2008.

Concerns persist that North Korea might carry out a third underground nuclear test after its much-hyped launch of a long-range missile fizzled in April. Media outlets have reported the North appears to have completed preparations for such a nuclear test.

North Korea's previous launches of long-range missiles in 2006 and 2009 were followed by nuclear tests. The international community has warned that the North, already under U.N. sanctions for the nuclear tests, will face tougher sanctions if it goes ahead with another test.

Late last month, the International Atomic Energy Agency said North Korea had made "significant" progress in building a light water nuclear reactor at its key nuclear complex in Yongbyon, citing satellite images.

South Korea is concerned the nuclear reactor under construction could be a cover to stockpile enriched uranium used in building nuclear weapons, although North Korea claims it is for producing electricity. (Yonhap News)