The phone calls, which took place on January 20, come after President Donald Trump announced that a location for his summit with Kim Jong Un -- which is to take place near the end of February -- has been decided.

Pompeo discussed the "next steps" on North Korean engagement with Japan's Foreign Minister Taro Kono, while he and South Korean Foreign Minister Kang Kyung-wha "updated each other" on engagements with Pyongyang, the State Department said.

Vice Chairman Kim Yong Chol, a right-hand man to the North Korean strongman, met Trump at the White House on Friday for an unusually long 90 minutes as the countries seek a denuclearization accord that could ease decades of hostility.

On Saturday, Trump said a "lot of progress" has been made on the issue.

Kim Jong Un and Trump first met in June in Singapore, where they signed a vaguely worded document in which Kim pledged to work toward the "denuclearization of the Korean peninsula."