By Agence France-Presse
Secretary of State Mike Pompeo held talks in an elegant Pyongyang guest house for a second day with North Korean leader Kim Jong Un's right-hand man Kim Yong Chol.
The US envoy later left Pyongyang bound for Tokyo, where he was to brief his Japanese and South Korean counterparts and talk to reporters on Sunday.
The negotiations followed President Donald Trump's summit with Kim Jong Un in Singapore, where the leaders signed a statement committing Pyongyang to "work towards complete denuclearisation of the Korean Peninsula".
While hailed by Trump as ending the threat of nuclear war, the June 12 statement was short on clear commitments, and Pompeo was tasked with negotiating a detailed plan in Pyongyang.
"Our policy hasn't changed," Pompeo's spokeswoman Heather Nauert told reporters as the meetings got underway.
"Our expectation is exactly what the president and Kim Jong Un jointly agreed to in Singapore, and that is the denuclearisation of North Korea," she said.
Saturday's talks were held at a villa in an official compound close to the imposing mausoleum where North Korea's former helmsmen Kim Il Sung and Kim Jong Il -- the current leader's grandfather and father -- lie in state.
As the day began, Pompeo left the compound to make a secure call to Trump away from potential surveillance, then returned to restart talks and they continued through a working lunch for almost six hours.
The meeting appeared to be drawing to a close at around 3.00pm (0600 GMT) and he flew out of the country just over an hour later, without talking to reporters.
In opening remarks, Kim Yong Chol asked Pompeo if he had slept well on his first overnight stay in the country, adding: "But we did have very serious discussion on very important matters yesterday.
"So thinking about those discussions you might have not slept well last night," he suggested.
Pompeo responded that he had slept "just fine" but the exchange suggested tougher talks ahead.
Pompeo warned that "the path toward complete denuclearisation building a relationship between our two countries is vital for a brighter North Korea and the success that our two presidents demand of us."
Kim replied: "Of course it is important. There are things that I have to clarify."
"There are things that I have to clarify as well," Pompeo responded.
Pompeo, who was on his third visit to Pyongyang, began the outreach when he was still Trump's CIA director and remained the pointman on negotiations after the process became public and he became secretary of state.
In comparison to past international nuclear disarmament negotiations, the discussions between Washington and North Korea on thawing ties and dismantling the North's arsenal appear to be proceeding in reverse.
Kim and Trump's Singapore summit resulted in a statement committing Pyongyang to "work towards complete denuclearisation of the Korean Peninsula" in exchange for US "security guarantees" and peace in the decades-old stand-off.
But rather than the two leaders crowning years of detailed negotiation with their one-on-one meeting, the short statement marked instead the start of a diplomatic long slog, and Trump earned the scorn of Korea watchers and non-proliferation experts when he declared the crisis over.
- 'Nitty gritty details' -
The task of establishing the disarmament programme now falls to Pompeo, who is seeking a formal declaration by the North of the size of its nuclear programme as well as an eventual timetable for it to be ended under international verification and inspection.
Many experts doubt Kim's sincerity -- a nuclear deterrent to US intervention has long been a strategic goal of his isolated, autocratic regime -- and few expect this to be a quick process, even if Washington wants results within a year.