Kim and Pompeo agreed to launch working-level negotiations led by North Korean Vice Foreign Minister Choe Son-hui and US Special Representative for North Korea Stephen Biegun.

But the talks have yet to begin, with no announcement on a date and location.

Meanwhile, Pompeo has said he hopes to meet with his North Korean counterpart next week to continue discussions on a potential second summit between US President Donald Trump and Kim.

The date and venue of that meeting are also undecided, the South Korean official said.

"I understand that they are continuing to plan for the high-level meeting," he said. "The North Koreans have not given a particular response."

Pompeo did not specify who his counterpart would be, but the official was skeptical that it could be the North Korean leader's sister, Yo-jong, who has been seen in most important meetings involving her brother.

"It's to be expected that North Korea is very careful with each step it takes," the official said. "It's a game where everything is at stake -- the abandonment of all the nuclear weapons and facilities the North has developed thus far -- so the North Koreans will be thoroughly prepared before a meeting."

He also backed recent reports that the second Trump-Kim summit is likely to be held early next year.

The first summit in Singapore in June produced a statement committing the North to work toward "complete" denuclearization of the Korean Peninsula in exchange for security guarantees from the US. (Yonhap)