The Washington Post earlier reported that the US officials had arrived at the northern side of Panmunjom on Sunday and their meetings were expected to continue on Monday and Tuesday.

Meanwhile, other Trump aides, including Joe Hagin, White House deputy chief of staff for operations, are traveling to Singapore for consultations with North Koreans largely on security measures and logistics related to the Singapore summit originally slated for June 12 and later canceled.

Chances are high that it will be held as initially agreed, given the revival of a rather positive tone especially in the wake of the surprise inter-Korean summit on the weekend, the second in a month.

If this week's dual-channel consultations between the North and the US fare well, Secretary of State Mike Pompeo may meet Kim Yong-chol, a senior North Korean Workers' Party official, to put the final touches to pre-summit talks.

Sung Kim's return to talks with North Korea is noteworthy for his expertise on the secretive communist regime.

It indicates the Trump administration's desire for success in dealing with Pyongyang.

Kim, currently ambassador to the Philippines, was a key player in the previous round of brisk nuclear negotiations on the North's nuclear program under the Bush administration.

In May 2008, when he served as director of the State Department's Korea office, he visited the North and crossed the Military Demarcation Line at Panmunjom into South Koreas carrying boxes loaded with documents on the North's activity at the Yongbyon nuclear complex for a verification process.

This was the result of the six-way nuclear talks, during which he met several times with Choe Son-hui.

In the Obama administration, he worked as the top US delegate to the now-defunct six-party talks before a three-year stint as ambassador to Seoul.

He then worked as the State Department's special representative for North Korea policy from 2014.

In February, he was promoted to the post of "career ambassador," a first for a Korea-born US diplomat.

He is fluent in Korean and English. As his career suggests, Kim is known as the sitting US official who is most versed in Korean affairs.

During a swearing-in ceremony for Kim as ambassador to Manila in late 2016, then-Secretary of State John Kerry said the envoy had "earned a reputation for sound judgment, for hard work, for great intelligence, and for deep humility."

Kerry quipped, "And the humility part is particularly impressive, given that he has also been called the George Clooney of the Foreign Service." (Yonhap)