US Secretary of State Mike Pompeo’s visit to Pyongyang left one thing clear: There will be long and arduous work ahead to completely remove the threat of North Korea’s nuclear arsenal and other weapons of mass destruction.

The only agreements the top US diplomat officially made during his two-day visit to Pyongyang last weekend was the establishment of working groups to discuss a denuclearization plan; working-level contacts on the shutdown of a missile engine test site; and talks on the repatriation of the remains American soldiers killed in the Korean War.

This means that despite Pompeo’s positive assessment of his talks with North Korean officials, the US side did not achieve its goal of pressuring or persuading the North to agree on an operational denuclearization road map and timeline.

Before Pompeo’s visit to Pyongyang, US national security adviser John Bolton said that he expected the secretary to discuss with the North Koreans a plan to dismantle their nuclear weapons, ballistic missile programs and biochemical weapons within a year.

Before landing in Pyongyang, Pompeo himself said: “On this trip, I’m seeking to fill in some details on these commitments and continue the momentum toward the implementation of what the two leaders promised each other and the world.”

What US President Donald Trump and North Korean leader Kim Jong-un promised in their historic summit in Singapore on June 12 was a complete denuclearization of the North. It is obvious that Pompeo failed his mission due to resistance from the North.

On his way to Tokyo from Pyongyang, Pompeo insisted that there was some progress in denuclearization talks.

“These are complicated issues, but we made progress on almost all the central issues,” he said, adding, “some places, a great deal of progress; other places, there’s still more work to be done.”

What we are worried about is that the denuclearization timeline and road map must have been the area in which “there’s still more work to be done.” The North may well have demanded US concessions on sanctions and a security guarantee.

The North Korean side’s statement denouncing the US side -- the first of its kind since the Singapore summit -- also heralds hurdles lying ahead of the US-NK denuclearization talks. The statement issued after Pompeo left Pyongyang on Saturday accused Washington of demanding “unilateral and gangster-like” denuclearization, pointing to the complete, verifiable and irreversible dismantlement.

The statement reiterated Pyongyang’s position on a “phased, synchronous” approach, saying it would be the shortest path toward realization of the denuclearization of the Korean Peninsula.

It is not unusual for the North to resort to such antagonism and accusations during a key negotiation, but the statement definitely shows that the two sides failed to narrow differences on the key issue of how to denuclearize the North and on what kind of timeline. The fact that Kim did not meet Pompeo, unlike in his two previous visits, should also be seen as part of the North’s strategy to engage in a tug-of-war with the US.

What should be noted is that despite the lack of progress in the denuclearization issue, both sides made it clear that they want to keep the dialogue momentum provided by the Singapore meeting.

Pompeo and his North Korean counterpart Kim Yong-chol exchanged letters addressed to Kim and Trump. The North Korean Foreign Ministry statement said that the North still had “trust” in Trump despite the disappointing talks in Pyongyang.

This attitude may reflect the fact that the North -- which has already benefited from the reconciliatory mood following Kim’s summits with South Korean President Moon Jae-in and Trump, including the suspension of major South Korea-US joint military exercises -- wants to keep the peace mood for now.

In this context, Pompeo did well when he agreed with his South Korean and Japanese counterparts in Tokyo on Sunday that the US will maintain sanctions against the North until its full denuclearization. As the three top diplomats also agreed, there should be no retreat on the goal of achieving a complete, verifiable and irreversible dismantlement of the North’s nuclear capacity, however arduous the work could be.