Biegun's trip has spawned speculation that he could visit the inter-Korean border truce village of Panmunjom for possible contact with North Koreans. But it remains to be seen whether such contact can materialize amid no signs of either side ceding ground.

On Monday, Biegun will meet his South Korean counterpart Lee Do-hoon to discuss how to keep up the momentum for dialogue with the North and make progress in joint efforts to denuclearize it and foster a lasting peace on the peninsula.

The US official also plans to pay a courtesy call on President Moon Jae-in on Monday, according to Moon's office.

It will be the second time that Moon bilaterally meets with Biegun, with the first such meeting taking place in September last year just days before Moon's trip to Pyongyang for a summit with North Korean leader Kim Jong-un.

According to Japanese broadcaster NHK on Sunday, Biegun told reporters upon leaving Washington that the United States has maintained its stance regarding the denuclearization of North Korea, and the communist country is also aware of that.

Asked about chances of his meeting with North Korean officials at Panmunjom, he declined to give comment, it added.

Concerns have persisted that the North could pivot away from the dialogue process as it has been ratcheting up tensions with a threat to take a "new way" if the year-end deadline is not met.

The US and the North last held working-level nuclear talks in Sweden in October. But the talks yielded little progress, with the North accusing the US of having come to the negotiating table "empty-handed."

Since then, Pyongyang has toughened its demands, telling the US to remove "all obstacles" that threaten the security of the North and hamper its development. The demands are seen as calls for sanctions relief and security assurances.

Recent weeks have seen a worrisome war of words between the US and the North.

On Tursday, the North upbraided the US for leading Wednesday's UN Security Council session on its military activities, which was widely seen as a warning that Washington could take steps such as tightening sanctions in the event that the regime conducts a long-range rocket launch.

Apparently mindful of Pyongyang's possible military provocations, US President Donald Trump has revived the threat of military action, and even said that North Korean leader Kim Jong-un could lose "everything" if he engages in hostile acts.

Biegun is currently in the process of securing congressional confirmation to become deputy secretary of state. (Yonhap)