He arrived in Seoul on Sunday for a three-day stay, his fourth visit here as Washington's point man on Pyongyang.

It came less than a week after he sat down with Lee in Washington.

The liberal Moon Jae-in government has been struggling to convince the people that it's in lockstep with the US in engaging the North.

US officials, however, are reportedly displeased with Seoul's push for speedy inter-Korean economic projects despite there being no further progress in efforts for a final, fully verified denuclearization of North Korea.

During a roundtable meeting with a group of South Korean reporters visiting the US capital last week, Bruce Klingner, senior research fellow at the Heritage Foundation, said US officials are upset about the Moon administration's pursuit of an easing of sanctions.

Secretary of State Mike Pompeo met with the North's leader Kim Jong-un in early October, but there have been no follow-up negotiations yet.

It remains unconfirmed whether Biegun plans to have talks with the North's Vice Foreign Minister Choe Son-hui during his ongoing visit to Korea.

He sought to meet her in Vienna but Choe did not respond to such overtures, according an informed source. (Yonhap)