North Korean leader Kim Jong Un inspects the Mount Kumgang tourist resort, North Korea, in this undated picture released by North Korea's Central News Agency (KCNA) on October 23, 2019. KCNA/REUTERS

Seoul, South Korea — The Swedish government was trying hard to convince the U.S. and North Korea to return to the nuclear negotiating table on Wednesday, but there were more signs that Kim Jong Un was in a confrontational mood. Sweden acts as an intermediary for the U.S. and North Korea, and the country's special envoy Kent Harstedt said Wednesday in Seoul that another formal invitation would be sent to both parties to resume working-level talks in Stockholm.

U.S.-North Korea talks have been largely stalled since a February summit between Kim and President Donald Trump ended in disagreement over the North Korean delegation's demands for sanctions relief in exchange for what the U.S. deemed to be insufficient steps toward dismantling the North's nuclear infrastructure.

Harstedt said he had "cautious optimism" that the U.S.-North Korean dialogue could be resumed with a new meeting of technical experts in Stockholm. That working-level discussion also broke down over disagreements several weeks ago. The Swedish envoy warned that it was "a historic opportunity that might not come again."

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Asked about the time frame for a possible resumption of the dialogue, Harstedt said it was up to the U.S. and North Korea to determine their responses to the invitation, but he was hopeful it would happen before the end of the year.

President Trump hinted on Monday that his administration was still pushing behind the scenes for a deal with North Korea to rid the country of its nuclear weapons.

"There's some very interesting information on North Korea," Mr. Trump said Monday. "A lot of things are going on. And that's going to be a major rebuild at a certain point."

North-South Korea relations deteriorate

South Korea's government has been a leading force in the push for the U.S. and North Korea to reach a deal for denuclearization, and ties between the neighboring nations had improved as Mr. Trump and Kim appeared to make headway last year. But as the U.S.-North Korean dialogue stumbled, the North-South relations nosedived.

North Korea's state-run media reported Wednesday that Kim had visited Mt. Kumgang, or Diamond Mountain, a North Korean tourist resort that South Koreans had been permitted to visit during times of more neighborly relations. Along with the jointly-run Kaesong industrial complex in North Korea, Mt. Kumgang was a powerful show of cross-border unity and cooperation.

But on Wednesday, Kim criticized the South Korean-made infrastructure at the resort as "shabby," and ordered it all torn down and replaced with new, modern facilities built by his government.

Kim's visit last week to another mountain sparked speculation that he might be about to make a significant move - either toward or away from negotiations with South Korea or the U.S. Kim was shown galloping on a white horse on Mount Paektu, a sacred peak linked strongly in North Korean propaganda to his family's ruling dynasty. He and his father have visited the mountain ahead of major events and announcements.

The South Korean Ministry of Unification seemed surprised by Kim's criticism over and plans for Mt. Kumgang. A spokesperson said the ministry had not received any official documentation about the changes announced by Kim, but that it was willing to "discuss the protection of the property rights of our people, the spirit of the inter-Korean agreement, and the resumption and activation of the tour program at any time."

For analysts in South Korea, it was a worrying sign that relations were deteriorating further.

"Even if the inter-Korean dialogue is to resume, I suspect that it would to be difficult for it to lead to an improvement in inter-Korean relations or a thaw," Cheong Seong-Chang, a lead researcher at the Sejong Institute in Seoul, told CBS News on Wednesday.

Cheong predicted that Kim might soon order the destruction of South Korean facilities and push for North Korean redevelopment of the Kaesong complex. "As such, inter-Korean relations have been further severed following the breakdown of the U.S.-North Korea negotiations, and it is questionable how serious and desperate the South Korean government is indeed taking the current situation."