The situation on the Korean Peninsula has seen a significant improvement since previous year after Kim boosted ties with South Korean President Moon Jae-in and held a historic summit with Trump in June.
Mr Kim has purged and replaced many top diplomats and officials who served his father and grandfather with new and younger advisers as he gears up to meet US President Donald Trump in Vietnam next week.
U.S. President Donald Trump shakes hands with North Korean leader Kim Jong Un at the Capella Hotel on Sentosa island in Singapore June 12, 2018.
"But Kim's style is a lot more popular among customers", he said.
In contrast to Bolton, Trump has voiced characteristically optimistic views on his role and the outlook of talks, saying he believes Kim wants change and that North Korea has the potential to become an economic powerhouse if full denuclearization is achieved. "This is an important step towards that ultimate goal", the official said.
"Kim Hyok Chol is a career diplomat too, but he apparently has passed a loyalty test to become the point man in the negotiations".
Cheong Wa Dae spokesperson Kim Eui-kyeom had earlier stated that Bolton and Chung would maintain close communication, when he announced that South Korean President Moon Jae-in and Trump would hold a telephone conversation regarding the upcoming summit.
The United States and North Korea will seek a common understanding of what denuclearization means when President Donald Trump presses Kim Jong Un next week to give up all of the North's nuclear weapons, USA officials said on Thursday.
North Korea's former ambassador to Spain Kim Hyok-chol has replaced the regime's Vice Foreign Minister Choe Sun-hui.
Mr Thae also said Mr Han had been purged, which means he was likely to have been sent to a labour camp for re-education or possibly executed.