BEIJING -- The top nuclear envoys of South Korea and China discussed North Korea's recent nuclear threat and agreed to bolster "strategic cooperation" to prevent Pyongyang from carrying out its fourth nuclear test, a Seoul diplomat said Saturday.

Hwang Joon-kook, Seoul's chief envoy to the six-party talks that also involve the United States, North Korea, Russia and Japan, held talks with his Chinese counterpart, Wu Dawei, in Beijing on Friday. The meeting came on the heels of three-way talks with the U.S. and Japan in Washington earlier this week.

Hwang and Wu reaffirmed a "clear commitment to oppose any North Korean provocations, particularly for an additional nuclear test, and agreed to deepen bilateral strategic communication and cooperation to curb such provocations," the diplomat with knowledge of the Friday talks said on the condition of anonymity.

"The two sides also agreed that the current situation on the Korean Peninsula is grave and worrisome following North Korea's threat of a nuclear test," the diplomat said.

In a move seen as part of stepped-up diplomacy to revive the long-stalled multilateral forum aimed at ending the North's nuclear program, Hwang and Wu also discussed "ways to resume meaningful dialogue to make progress in denuclearizing North Korea and prevent it from sophisticating its nuclear technology," according to the diplomat.

The Beijing talks came as South Korean officials voiced "flexibility" in preconditions for the six-nation talks, indicating that they could lower the bar for North Korea to sit down at the negotiating table.

In Washington on Friday, the U.S. State Department said the Chinese nuclear envoy Wu will visit the U.S. from Monday and hold talks with his U.S. counterpart Glyn Davies.

Davies and Wu will meet in New York for two days starting Monday, and then again in Washington on Thursday, according to a statement released by the U.S.

"Wu's visit is part of a series of high-level, in-depth U.S.-China discussions on how to achieve our shared goal of a denuclearized North Korea in a peaceful manner," the statement said.

Since its third nuclear test in February last year, North Korea has repeatedly expressed its willingness to reopen the six-party talks "without preconditions," but South Korea and the U.S. have maintained that North Korea must first demonstrate its sincerity toward denuclearization before the disarmament-for-aid talks can resume.

China has been more accommodating toward North Korea, urging South Korea and the U.S. to lower their bar for talks.

Fresh diplomatic moves have been under way to resume the six-party forum that has been dormant since late 2008. During this week's trilateral meeting in Washington, the top nuclear envoys of South Korea, the U.S. and Japan agreed to lower the bar for North Korea to rejoin the six-party forum, Seoul officials said.

After showing signs of diplomacy, North Korea has again turned hostile in recent weeks, conducting live-fire drills near the tense Yellow Sea border with South Korea and warning of a "new form" of nuclear test. (Yonhap)