The top diplomats of South Korea, the United States and Japan had talks in Seoul on Thursday on North Korea, emboldened by the first-ever Pyongyang-Washington summit talks.

Starting a bilateral meeting with US Secretary of State Mike Pompeo, South Korean Foreign Minister Kang Kyung-wha expressed hope that "the current momentum will be maintained."

Their closed-door talks were followed by a trilateral session involving Japan's Minister Taro Kono.

Earlier in the day, Pompeo paid a courtesy call on President Moon Jae-in at his office Cheong Wa Dae.

The secretary briefed them "in detail" on the results of the summit meeting between President Donald Trump and the North's leader Kim Jong-un held in Singapore on Tuesday, officials said.

In a joint statement, Kim agreed to the "complete denuclearization" of the Korean Peninsula and Trump vowed security guarantees for the communist nation on the basis of the "new relations" between the longtime adversaries.

Pompeo will lead Washington's follow-up negotiations with Pyongyang, of which schedule has not been announced yet.

"I will be the person who takes the role of driving this process forward," he told reporters.

He's expected to sit down with a high-level North Korean official as early as next week. 

He said the denuclearization process can make significant progress by the end of Trump's first term in early 2021.

On the outlook for "major disarmament," the former CIA director said, "We're hopeful that we can achieve that in the next 2 1/2 years, something like that."

He dismissed criticism about the summit accord without the term "compete, verifiable and irreversible denuclearization".

"Let me assure you that the 'complete' encompasses verifiable in the minds of everyone concerned," he stressed. "One can't completely denuclearize without validating, authenticating."(Yonhap)