The United States has explicitly confronted North Korea about suspected secret nuclear weapons facilities during ongoing denuclearization negotiations, a commentary published over the weekend by the North’s state-run media has appeared to show.

In the commentary released Saturday, the Rodong Sinmun, the newspaper of the North’s ruling Workers’ Party, blasted “those opposed to dialogue” in the U.S., saying that officials both inside and outside the White House had “provided the negotiating team with a truncheon called (the) ‘theory of suspected north Korea’s secret nuclear facilities,’ a fiction, driving it to derailing dialogue.”

Since U.S. President Donald Trump’s landmark June meeting in Singapore with North Korean leader Kim Jong Un, a steady trickle of reports citing U.S. intelligence and other sources have claimed that Pyongyang has continued to boost its nuclear fuel production and missile capabilities at multiple secret sites despite a denuclearization pledge agreed to at the historic meeting.

At the Singapore summit, Kim and Trump reached a vague agreement to “work towards the complete denuclearization of the Korean Peninsula.” But while talks have continued, including a visit in early July to Pyongyang by U.S. Secretary of State Mike Pompeo, there has been little movement since the Kim-Trump meeting.

Saturday’s commentary, which appeared to confirm for the first time that the U.S. side had challenged the North over its alleged secret nuclear sites, may shed some light on why progress on denuclearization has stalled.

Pyongyang has bristled at the reports of secret sites, instead seeking to shift the focus to its own push for a phased, simultaneous approach to denuclearization.

The commentary, summarized in English by the state-run Korean Central News Agency, blamed Trump opponents and hard-liners for the “deadlock” in the denuclearization talks, and urged the president to act boldly to make progress on the thorny issue.

In a pattern often repeated in North Korean state media since the Singapore summit, Pyongyang has been careful not to blame the U.S. president himself for the slow progress. Instead, it has used its mouthpieces to lavish praise on Trump while also urging him to take more audacious steps in response to its own “goodwill measures.” In particular, Pyongyang has stepped up demands that Washington agree to declare an end to the 1950-53 Korean War as part of steps toward a formal peace treaty.

Trump “has a ‘dream’ about world peace, an epoch-making cause,” Saturday’s commentary said, but he “has too many rivals.” The “present deadlock,” it went on, “demands a bold decision on the part of President Trump.”

Andrew O’Neil, an expert on North Korea and a professor at Griffith University in Australia, said it was “highly plausible” that the U.S. had confronted the North for its ongoing nuclear and missile activity, noting a similar instance 16 years ago, when senior American diplomat James Kelley confronted his North Korean counterparts with American intelligence data suggesting a secret nuclear project was underway at the time.

“The U.S. has done this before in bilateral talks — in 2002 when Assistant Secretary of State Kelly called out the North Koreans on uranium enrichment and publicly announced the accusation, which in turn triggered a tougher U.S. posture,” O’Neil said.

It was not clear how Pyongyang would react to the latest accusations, but Van Jackson, a North Korea expert at Victoria University of Wellington in New Zealand, said that any confrontation over the secret sites by the White House would “only produce bad outcomes for the U.S.”

Jackson said that the North Koreans currently believe they can successfully “drive a wedge between Trump and the rest of his administration,” but that if this thinking falters, the two sides would likely see a return to last year’s tense security environment that took the two nations to the brink of war.

Pointing to past moves by Pyongyang to exploit its rivals for material and symbolic gains, he said it is difficult not to see similarities in its approach to Trump.

“There are some who still hold out hope that’s not what’s happening here,” Jackson said. “But it’s hard to read propaganda statement after statement trying to pump up the idea that Trump is surrounded by enemies and the North Koreans are his only real friends.

“They’re obviously appealing to Trump’s ego — as every other foreign leader has by now learned — and so far it’s working,” he added.

Pyongyang has touted its own moves, including a halt to nuclear and missile testing, the destruction of its main nuclear test site and the handing over of remains of U.S. troops killed in the Korean War, as justifying reciprocal measures by Washington.

When Kim met South Korean President Moon Jae-in in April for the first of two summits held so far this year, the pair agreed to push for a declaration of an end to the Korean War before the year’s end. U.S. officials, however, have insisted that the North relinquish its nuclear weapons before such a move.

On Saturday, South Korea’s Korean Broadcasting System reported that the U.S. had even proposed that the North ship half of its nuclear warhead stockpile to the United Kingdom, which is known for its expertise in nuclear weapons dismantlement.

That report, which cited an unidentified diplomatic source, said a U.S. State Department official who had recently visited South Korea said the proposal came after Pompeo requested British technical support for the endeavor during talks in June with Britain’s then-Foreign Secretary Boris Johnson.

The veracity of the report could not be confirmed, but before any such transfer, the U.S. is almost certain to ask the North for a list detailing its nuclear weapons.

Pyongyang has criticized Washington for its strict stance, calling its demands for the complete, verifiable and irreversible dismantling of its nuclear arsenal as “gangster-like” and “unilateral.”

In Saturday’s commentary, it also urged Pompeo, who is widely expected to visit the North again sometime next month, to brush aside speculation that the North intends to maintain at least part of its arsenal.

The top U.S. diplomat, it said, “should not be forced to meet a ‘miserable destiny’ but resolutely smash the opposition’s unreasonable and foolish assertions with his own view and courage and display his wisdom and bargaining power . . . in order to realize the president’s will.”

Pompeo, whose visit would be his fourth to the country, said Thursday that his team was “continuing to make progress” with the North, and expressed hope that “we can make a big step here before too long.”