The US president is set to arrive in Seoul on Saturday following his attendance at the Group of 20 summit in Osaka, Japan, on Friday and Saturday.

Biegun's trip comes amid renewed hopes for the resumption of nuclear talks between Washington and Pyongyang that have been at an impasse since the no-deal summit between Trump and North Korean leader Kim Jong-un in Hanoi in February.

This month, Trump and Kim exchanged personal letters, which bolstered expectations that the US and the North could resume their working-level talks to bridge differences and pave the way for a possible third summit.

In a written interview with Yonhap News Agency and six other global news outlets, Moon said that the US has been engaged in behind-the-scenes dialogue with the North for a possible third summit while noting that the Korea peace process is making steady progress.

During his stay through Sunday, Biegun could meet other top Seoul officials, including those at the presidential office Cheong Wa Dae.

Speculation has also persisted that he could travel to the inter-Korean border truce village of Panmunjom inside the Demilitarized Zone to meet with North Korean officials. There is still no official word on that possibility.

During an event at the Atlantic Council think tank earlier this month, Biegun emphasized that the "door is wide open" to negotiations with the North and without preconditions.

He also noted that both sides understand the need for a "flexible approach" -- remarks that some observers said insinuated the US' willingness to ease its hard-line stance.

A major bone of contention is the extent of Pyongyang's denuclearization in return for Washington's sanctions relief.

During the Hanoi summit, Kim offered to dismantle the mainstay Yongbyon nuclear complex, but Trump wanted more than the complex, which the US sees as only a part of the North's sprawling nuclear program.

In the recent interview, Moon said that if the North completely dismantles the Yongbyon complex, it is "possible to say that the denuclearization of North Korea has entered an irreversible stage."

It was the first time that Moon has publicly characterized Yongbyon's dismantlement as the starting point of irreversible denuclearization that could lead to sanctions relief in return. (Yonhap)