South Korea's top nuclear envoy left for China Wednesday, a senior official said, as Seoul deepens efforts to convince the U.N. Security Council to adopt tougher sanctions against North Korea's third nuclear test.

Lim Sung-nam, Seoul's chief envoy to the six-party talks aimed at ending the North's nuclear ambition, will meet with his Chinese counterpart Wu Dawei later Wednesday during his two-day visit to Beijing, the foreign ministry official said on the condition of anonymity.

"During the meeting, Lim will request China's cooperation with regard to a U.N. response to North Korea's third nuclear test," the official said.

It will be the first meeting between Lim and Wu since South Korean President Park Geun-hye took office early this week.

North Korea defied international warnings by conducting its third nuclear test on Feb. 12, raising fears that Pyongyang might be a step closer to a workable long-range nuclear missile.

Seoul and Washington are seeking to convince the U.N. Security Council to adopt a resolution against Pyongyang that would include Articles 41 and 42 of Chapter 7 of the U.N. Charter, which allows all U.N. members to enforce sanctions by military means.

If passed, the resolution will theoretically enable navy ships to intercept and board North Korean vessels suspected of carrying illicit weapons or nuclear and missile components.

South Korean diplomats have admitted that China, the North's last-remaining ally and one of the veto-wielding council members, has expressed opposition to including Chapter 7 in the new resolution. (Yonhap News)