Korea watchers have been divided on how Biegun's promotion will affect the negotiations with Pyongyang, with some saying it will elevate the issue to a higher US foreign policy priority.

Others have expressed concern the larger portfolio will turn his attention away from the talks. Biegun may also have to fill in for US Secretary of State Mike Pompeo if the top American diplomat decides to run for the Senate next year as widely rumored.

The envoy assumed his role in August last year following the June summit between US President Donald Trump and North Korean leader Kim Jong-un, where the two leaders agreed to pursue complete denuclearization of the Korean Peninsula in exchange for US security guarantees.

Biegun has since led efforts to implement the deal, including through two additional meetings between Trump and Kim in February and June, but negotiations have faltered amid wide gaps over how to match the North's denuclearization measures with US concessions.

There is speculation Biegun may seek a meeting with his North Korean counterpart during his stay in Beijing through Friday.

A State Department spokesman told Yonhap News Agency earlier he had no "additional travel or meetings to announce."

An offer by Biegun to meet with the North Koreans during his stay in South Korea earlier this week went unanswered.

Meanwhile, concerns have grown that North Korea may launch a long-range missile in the coming weeks unless the US acquiesces to its demands for sanctions relief and other concessions before the year-end deadline set by Kim Jong-un. (Yonhap)