SEOUL, South Korea — A meeting between U.S. Secretary of State Mike Pompeo and a senior North Korean envoy has been delayed, throwing stalemated diplomacy over the North's nuclear weapons into further uncertainty.

The State Department said in a short statement Wednesday the officials would meet later "when our respective schedules permit." It offered no reason, and North Korea's propaganda services have not mentioned the meeting.

After last year's fears of war, North Korea and the United States are trying to revive stalled diplomacy meant to rid the North of its nuclear weapons. There was much talk of the possibility of success following a meeting in June between U.S. President Donald Trump and North Korean leader Kim Jong Un, but in the months since there has been little to quiet skeptics who believe the North will never give up weapons it has described as necessary to counter a hostile Washington.

Pompeo was supposed to travel to New York on Thursday to meet with his North Korean counterpart, Kim Yong Chol. The U.S. State Department earlier said the top U.S. envoy for North Korea, Stephen Biegun, was to join Pompeo and Kim to discuss how to get to what it calls "achieving the final, fully verified denuclearization" of North Korea.

South Korean presidential spokesman Kim Eui-kyeom said later Wednesday that his government doesn't believe U.S.-North Korea negotiations have completely broken down or "lost their momentum" because of the postponement. Seoul's Foreign Ministry also expressed hope that the U.S. and North Korea can quickly reschedule a high-level meeting.

South Korea's presidential Blue House said the United States had informed it of the talks' postponement in advance. But the Blue House would not reveal the reason for the postponement, referring questions to the State Department.

News of the postponement came after North Korea's Foreign Ministry criticized the U.S. on Friday for its continued support of sanctions and hinted it may resume nuclear development.

In a statement, North Korea warned it could bring back Kim Jong Un's "byongjin" policy of simultaneously advancing its nuclear arsenal and its economic development if the United States doesn't change its stance. The North stopped short of threatening to abandon nuclear negotiations with Washington.

Koh Yu-hwan, a North Korea expert at Seoul's Dongguk University and a policy adviser to South Korean President Moon Jae-in, said a high-level meeting between the U.S. and North Korea immediately after the U.S. midterm elections was never realistic, especially when the North was in no mood to make any concrete concessions.

Trump's engagement with North Korea in recent months was apparently timed to the midterms, but he will no longer agree to major meetings if there are no realistic expectations of progress in nuclear diplomacy, Koh said.