The U.S.' top nuclear envoy met with representatives from UN Security Council member states, as well as South Korea and Japan, on Wednesday ahead of a council meeting on North Korea.

During a luncheon at the U.S. Mission to the United Nations, Special Representative for North Korea Stephen Biegun reportedly stressed the severity of the current situation, calling for a unified front against the North's provocations.

Biegun is also arranging to visit the Korean Peninsula next week to speak with South Korean officials and to seek a meeting with the North Korean side.

Pyongyang has ratcheted up tensions as its end-of-year deadline for Washington to offer more concessions in their stalled denuclearization talks draws near.

Earlier in the week, Pyongyang said it conducted a "very important test," presumed to be a rocket engine experiment, at its Tongchang-ri satellite launch site, raising speculation that it may be gearing up for a possible intercontinental ballistic missile test.