US Secretary of State Mike Pompeo has brushed off North Korean accusations of "gangster-like" diplomacy during negotiations in Pyongyang, saying he will pursue denuclearisation talks.
Pompeo said in Tokyo on Sunday there was still a lot of work to do, but he was confident North Korean leader Kim Jong Un would stick to a commitment to abandon nuclear weapons that he made during a summit with US President Donald Trump in Singapore last month.
Pompeo met with Japan's Minister of Foreign Affairs Taro Kono and South Korean Foreign Minister Kang Kyung-wha after two days of talks in Pyongyang that ended on Saturday.
"When we spoke to them about denuclearisation, they did not push back," Pompeo told a news conference.
"The road ahead will be difficult and challenging and we know that critics will try to minimise the work that we've achieved."
Pompeo spoke after North Korea's foreign ministry said he had presented a "unilateral and gangster-like" demand for "complete, verifiable and irreversible" denuclearisation.
Kim made a broad commitment in Singapore to "work toward denuclearisation" but did not give details on how or when he would dismantle North Korea's nuclear program. Trump in turn offered security guarantees to Pyongyang and pledged a halt to large-scale military drills with South Korea.
North Korea's latest comments, which came after Pompeo said talks had made progress, are a reminder of the difficulties that previous US administrations have had negotiating with the reclusive state and suggest that Pyongyang may not agree to any rapid denuclearisation.
Leaked US intelligence findings concluded that North Korea does not intend to give up its nuclear program completely.
Japan's Kono thanked Pompeo and said the three allies had reaffirmed a commitment to keeping sanctions on North Korea until it abandoned nuclear weapons and ballistic missiles of all ranges.
"We confirmed that security assurances will be provided to North Korea as agreed in the summit. At the same time we have reaffirmed that the international community will continue to fully implement relevant UN Security Council resolutions," Kono said.
Pompeo said before leaving for Pyongyang he was seeking to "fill in" details on North Korea's commitments and maintain the momentum towards implementing the Singapore agreement between Trump and Kim.
US intelligence officials earlier told Reuters Pompeo wanted to agree on at least an initial list of nuclear sites and an inventory that could be checked against available intelligence.
"There is still much work to do to establish what the precise timeline of the various events will be," Pompeo said in Tokyo.
Pompeo said he had also pushed North Korea on a promise to destroy a missile engine test site and that the United States would like that to happen "soon".