Top nuclear envoys of South Korea and the U.S. discussed North Korea issues on the phone Wednesday after North Korean leader Kim Jong-un warned he would unveil a "new strategic weapon."

According to a Foreign Ministry official, South Korea's chief nuclear envoy Lee Do-hoon and U.S. Deputy Secretary of State Stephen Biegun exchanged their assessments of Kim's remarks made during a four-day Central Committee meeting of the North's ruling Workers' Party.

The two sides also discussed ways to resume talks between Washington and Pyongyang. 

Lee will reportedly visit the U.S. later this month to meet with Biegun and continue discussions on the North's denuclearization. 

Earlier on Wednesday, North Korean state-run media reported that Kim said there are no grounds for him to keep his promise to suspend nuclear and long-range missile tests, vowing to unveil a "new strategic weapon" soon.