US Secretary of State Mike Pompeo Thursday said America was prepared to engage immediately in negotiations with North Korea to transform relations and to achieve the denuclearization of Pyongyang by 2021.

His comments came after North Korean leader Kim Jong Un agreed to make a historic visit to South Korea soon and close a missile testing site in the presence of international inspectors in a meeting with President Moon Jae-in in Pyongyang on Wednesday.

Pompeo, in a statement, welcomed Moon and Kim's reaffirmation of the Singapore joint statement of complete denuclearisation of the Korean Peninsula, including the permanent dismantlement of all facilities at Yongbyon in the presence of the US and the International Atomic Energy Agency (IAEA)inspectors.

"This will mark the beginning of negotiations to transform the US-DPRK relations through the process of rapid denuclearisation of North Korea, to be completed by January 2021, as committed by Chairman Kim, and to construct a lasting and stable peace regime on the Korean Peninsula," he said.

"We also welcome Chairman Kim's decision to complete the previously announced dismantlement of Tongchang-ri site in the presence of US and international inspectors as a step toward the final fully verified denuclearisation of North Korea, as agreed by Chairman Kim at the Singapore summit with President Trump," Pompeo added.

On the basis of these important commitments, he said, the US was prepared to engage immediately in negotiations to transform its relations with North Korea.

Pompeo said he has invited South Korean Foreign Minister Ri Yong Ho to a meeting in New York City next week, where they both are already scheduled to be in attendance at the United Nations General Assembly.

"Likewise, we have invited North Korean representatives to meet our Special Representative for North Korea, Stephen Biegun, in Vienna, Austria, at the earliest opportunity," he added.