TOKYO — In a sharp signal that denuclearization negotiations with North Korea will be drawn out and difficult, Pyongyang on Saturday lambasted the U.S. stance as regrettable, gangster-like and cancerous, directly contradicting Secretary of State Mike Pompeo’s rosy assessment that his two days of talks had been “productive.”

A harsh statement from an unnamed spokesman for the Foreign Ministry was carried on the state-run Korea Central News Agency just hours after Pompeo left Pyongyang on Saturday and told reporters that significant progress had been made “in every element” of what he characterized as “good-faith negotiations.” Pyongyang crushed that appraisal, saying the United States had betrayed the spirit of the June 12 Singapore summit between President Trump and North Korean leader Kim Jong Un.

“The U.S. side came up only with its unilateral and gangster-like demand for denuclearization,” the statement said.

“The issues the U.S. side insisted on during the talks were the same cancerous ones that the past U.S. administrations had insisted on,” it added.

Though North Korea still has faith in Trump, the statement said, it warned that the U.S. approach had brought the two countries to a “dangerous” stage that could “rattle our willingness for denuclearization.”

It was unclear whether the North Korean statement represented potential doom for meaningful negotiations, as some analysts believed, or was just Pyongyang’s standard negotiating style, as others asserted. It exposed the fragility of discussions at the center of Trump’s foreign policy and raised questions about Pyongyang’s intentions.

At the very least, the statement was an embarrassment for Pompeo, who has repeatedly said Kim has assured him personally that North Korea is willing to give up its nuclear weapons. But Pompeo did not meet with the North Korean leader on this trip, as he did on two previous visits and as some administration officials had hoped he would this time as well.

In its return to pre-Singapore bellicose rhetoric, the ministry’s statement also served as a rebuttal to Trump, who has declared the North Korean nuclear threat over and done with, even though nothing in the joint declaration signed in Singapore was definitive. The two countries do not even agree on what the concept of denuclearization means.

Some analysts saw no reason for alarm in Pyongyang’s downbeat version of events, considering it a routine North Korean negotiating tactic rather than a full-blown retreat from Pyongyang’s seeming commitments.

“They’re upping the ante for what they want, and downplaying what we want,” said Bill Richardson, who has negotiated with North Korea for prisoner releases. “This is typical. They’re very skilled at sending messages. And their message is that this negotiation is not going to be easy. And it’s going to be very costly. So you’d better be prepared to deliver.”

But Evans Revere, a former U.S. diplomat with a long history of negotiating with North Korea, said it was evident that the talks in Pyongyang had not gone well — and that it appears North Korea may have no intention of actually denuclearizing in the way the United States would want.

“Pompeo appears to have presented the North Koreans with some demands and requirements for real moves toward denuclearization, as opposed to the symbolic steps and empty language Pyongyang has been using so far. He deserves credit for doing so,” Revere wrote in an email.

“But in doing so, he has elicited North Korean ire, and he has now seen the reality of North Korea’s game plan and intentions that many of us have been describing for some time,” Revere added. “Welcome to our world, Mr. Secretary.”

Pompeo has come under increasing pressure to produce results, with Trump having touted the summit as a game-changing moment that eliminated North Korea’s nuclear threat. The State Department announced the formation of a small working group to work on details. Richardson counseled patience, endurance ­­and restraint.

“The president needs to restrain himself from declaring ‘Mission Accomplished’ when the mission hasn’t really started,” he said.

Pompeo went to Pyongyang hoping to formalize details of what actions North Korea is committed to taking to show its intention to denuclearize. Pyongyang has said it expects sanctions to be lifted in stages as it takes steps toward that goal, though Washington has insisted there will be no sanctions relief until the process has been completed. But the “maximum pressure campaign” the administration adopted to squeeze the North Korean economy through sanctions has eased somewhat already, particularly along the border with China.

Expectations were buoyed in part by national security adviser John Bolton, who said last week that North Korea could accomplish the “bulk” of its denuclearization within a year. Pompeo has been more circumspect, estimating that it will take until the end of Trump’s first term in office, or two and a half years.

“The expectation that Pompeo was going to come home with a dramatic deliverable was unrealistic to start,” said Daryl Kimball, executive director of the Arms Control Association.

“Yeah, technically, it could be done in a year if North Korea didn’t have its own ideas about the pace and what the United States needs to do to get there. What we’re seeing is the reality of negotiations. It’s not surprising to see the North Koreans push back in reminding the United States it has some steps to take in order to help build a peace regime on the Korean Peninsula.”

Analysts say that any final accord between the two nations to eliminate Pyongyang’s sophisticated nuclear and missile arsenal will be a long slog with no guarantee of success.

“While we were hopeful there would be some sort of breakthrough, it seems both sides can’t even agree to what transpired after countless hours of talks — and that is a massive problem,” said Harry Kazianis, an Asia expert at the Center for the National Interest.

Pompeo told reporters Saturday that the two countries would soon hold working-level talks on the destruction of Pyongyang’s testing facility for missile engines. He also said Pentagon officials will meet with their North Korean counterparts on or around July 12 at the demilitarized zone between the Koreas to discuss the return of the remains of U.S. military personnel who died during the Korean War.

Last month, Trump told a crowd of supporters that the remains of 200 service members had “been sent back,” but U.S. military officials later said that was not the case. U.S. officials viewed the handing over of remains as an easy confidence-building measure for North Korea to demonstrate its sincerity, and they have been frustrated with the slowness of Pyongyang’s follow-through.

Ahead of the new round of talks, Kim Yong Chol, North Korea’s septuagenarian former spy chief, teased Pompeo, suggesting that the “serious” negotiations the night before may have caused Pompeo to lose sleep.

“We did have very serious discussion on very important matters yesterday. So thinking about those discussions, you might have not slept well last night,” Kim Yong Chol said.

“Director Kim, I slept just fine,” Pompeo responded, according to a pool report provided by reporters accompanying the secretary of state.

Kim Yong Chol, a regime hard-liner who is careful not to act outside Kim Jong Un’s instructions, said he needed to “clarify” aspects of his nearly three-hour negotiations Friday with Pompeo, a desire the top U.S. diplomat immediately echoed.

“There are things that I have to clarify as well,” Pompeo said.

The display of small talk between North Korean and U.S. officials, a rarity given the infrequent contacts between the longtime adversaries, revealed both the tension at the heart of the nuclear negotiations and the increasing familiarity of the two men, who have become diplomatic counterparts during Pompeo’s three visits to Pyongyang and Kim Yong Chol’s visit to the United States in May.

State Department spokeswoman Heather Nauert said Pompeo had been “very firm” in seeking three basic goals from the visit: the complete denuclearization of North Korea, security assurances and the repatriation of fallen soldiers’ remains.

Diplomats, who spoke on the condition of anonymity to discuss sensitive conversations, said the United States continues to struggle to develop a shared understanding of what denuclearization means to North Korea. Maintaining even basic communications has been difficult.

Adding to the pressure on Pompeo is a leaked U.S. intelligence assessment casting doubt on North Korea’s willingness to relinquish its arsenal.

Nauert said Pompeo called Trump on Saturday morning to update him on the talks, a conversation that included Bolton and White House Chief of Staff John F. Kelly.

Analysts say there are likely to be many more calls like this in the months and probably years to come.

“The North Korea threat still exists,” Kimball said. “North Korea continues to improve its arsenal. This is just the beginning of a long process.”

Morello reported from Washington. Adam Taylor in Seoul contributed to this report.