Sanctions will remain on Pyongyang until the regime denuclearizes, the United States' ambassador to South Korea on Thursday insisted ahead the upcoming summit between the US and North Korea.

Harry Harris was speaking at a forum in Seoul where he discussed the meeting that will be held between US President Donald Trump and North Korean leader Kim Jong-un in Hanoi, Vietnam, on Feb. 27 and 28 to advance the dialogue on disarmament.

“The United States and our South Korean ally are in complete agreement that sanctions will remain until DPRK denuclearizes,” he said in a statement cited by Yonhap news agency.

"Our goal remains the same: to achieve our shared objective of a final, fully verified denuclearization of the DPRK as committed (to) by Chairman Kim in Singapore," he added.

Kim and Trump met for the first time in Singapore last year to discuss North Korea disarmament.

A joint agreement was issued after the meeting but the vague wording, which states that Kim commits “to work towards the complete denuclearization of the Korean Peninsula,” does not allow the two sides to achieve significant progress due to the lack of concrete steps.

It is expected that the second summit will serve to refine differences and clearly agree on what kind of disarmament Pyongyang would be willing to carry out and in what terms it could comply, as well as to establish compensation measures from Washington.

Pyongyang has requested compensation such as aid, the lifting of sanctions and the signing of a peace treaty to end the state of war which still technically prevails over the Korean Peninsula since the end of the conflict that devastated the region between 1950 and 1953.

Harris, however, added an optimistic note to his speech and assured that North Korea could expect a "brighter, more secure and more prosperous future," if it fulfills its denuclearization promise.

He also credited South Korea’s President Moon Jae-in for his role in the groundwork for peace, as well as Beijing.

“Without China's support on sanctions, we wouldn't have achieved (the) progress that we have made so far," he said.