"Made it to Vietnam for President @realDonaldTrump's #HanoiSummit with the DPRK," Pompeo tweeted, referring to North Korea by its official name, the Democratic People's Republic of Korea. "Will be important opportunity to make progress on Singapore Summit commitments of transformed relations, building lasting peace, and complete denuclearization."

Trump and Kim are due to meet in Hanoi on Wednesday and Thursday to follow up on their first summit in Singapore in June.

The two leaders agreed then to work toward complete denuclearization of the Korean Peninsula in exchange for US security guarantees.

This week's summit is expected to flesh out steps both sides will take to achieve those goals.

The State Department said Pompeo is scheduled to meet with Vietnamese Deputy Prime Minister and Foreign Minister Pham Binh Minh in the evening.

Also possible is a meeting between Pompeo and his North Korean counterpart, Kim Yong-chol, for last-minute preparations ahead of the summit.

"Continuing our work to make progress toward denuclearization and furthering relations," he wrote in an earlier tweet en route to Hanoi. (Yonhap)