TOKYO - North Korean leader Kim Jong Un offered Wednesday to permanently dismantle the country's main nuclear site, but only if the United States makes concessions first.
President Donald Trump called the developments encouraging but made no new commitments.
Leaving the White House on Wednesday, Trump said that "we're making tremendous progress with respect to North Korea" and took credit for changing a dynamic under which he said it once seemed "inevitable" that the United States would go to war with the country.
Now he and Kim have a cordial relationship that included a "tremendous letter" from the North Korean leader this week, Trump said.
"It's very much calmed down," he said. "We're talking. It's very calm. He's calm. I'm calm."
Kim and South Korean President Moon Jae-in have been meeting in Pyongyang in an attempt to push forward their peace process, as well as advance dialogue with the United States. Standing side by side after their second day of talks, they declared that they had made a major step toward an "era of peace and prosperity" on the Korean Peninsula.
Kim pledged to visit the South Korean capital, Seoul, in what would be a first for a North Korean leader. He also pledged to allow in "external inspectors" to verify that a key missile test site has been disabled.
Later, Moon, who has fervently pursued engagement with the North, made history by addressing an audience of 150,000 people at a performance of the "mass games," North Korea's synchronized gymnastics and dance show.
"We have lived together for 5,000 years and been separated for 70 years, " he told the audience in the huge May Day Stadium. "We must live together as one people."
The talks were supposed to enhance cooperation between the two Koreas, as well as pave the way for a second summit between Kim and Trump later this year.
Experts said it was far from clear that Kim had made concessions that would make a summit an attractive proposition for the U.S. administration, but Trump himself reacted positively, calling the news "very exciting" on Twitter.
Kim Jong Un has agreed to allow Nuclear inspections, subject to final negotiations, and to permanently dismantle a test site and launch pad in the presence of international experts. In the meantime there will be no Rocket or Nuclear testing. Hero remains to continue being........
- Donald J. Trump (@realDonaldTrump) September 19, 2018
....returned home to the United States. Also, North and South Korea will file a joint bid to host the 2032 Olympics. Very exciting!
- Donald J. Trump (@realDonaldTrump) September 19, 2018
"We had very good news from North Korea, South Korea. They met, and we had some great responses," Trump told reporters at the White House on Wednesday morning.
"A lot of tremendous things. But very importantly, no missile testing, no nuclear testing," Trump said.
He noted with apparent approval that the latest inter-Korean summit included a proposal for a potential joint North Korean-South Korean bid for the Olympic Games, adding, "We have a lot of very good things going."
Trump said nothing about a potential second summit with Kim, with whom he met in Singapore in June.
Trump is expected to meet with Moon on Monday in New York, when both attend the annual United Nations General Assembly. Moon is expected to use the meeting to urge further U.S.-North Korean engagement.
In Pyongyang, Kim focused on relations with South Korea. The two Koreas are still technically at war 65 years after an armistice ended the Korean War.
"We have agreed to make the Korean Peninsula a land of peace that is free from nuclear weapons and nuclear threat," Kim said. "The road to our future will not always be smooth, and we may face challenges and trials we can't anticipate. But we aren't afraid of head winds because our strength will grow as we overcome each trial based on the strength of our nation."
Talks between the United States and North Korea have reached an impasse over who should make the next move. Washington wants Pyongyang to take a meaningful step toward dismantling its nuclear weapons program. North Korea, however, is pushing for the United States to declare the 1950-1953 Korean War formally over, and claims Trump made a promise to that effect in Singapore.
Members of Trump's own administration are known to be more wary about North Korea's intentions.
And Republican Sen. Lindsey Graham, S.C., a Trump political ally who is influential on national security, tweeted that he was concerned Moon's visit would undermine efforts by Secretary of State Mike Pompeo and U.N. Ambassador Nikki Haley to impose "maximum pressure" on Pyongyang through sanctions.
"While North Korea has stopped testing missiles and nuclear devices, they have NOT moved toward denuclearization," he tweeted.
I’m concerned South Korea’s visit is going to undermine efforts by @SecPompeo and Ambassador @nikkihaley to impose maximum pressure on the North Korean regime.
While North Korea has stopped testing missiles and nuclear devices, they have NOT moved toward denuclearization. https://t.co/VRnr6tn8dg
- Lindsey Graham (@LindseyGrahamSC) September 18, 2018
In a joint statement, North Korea pledged to "permanently dismantle" a missile engine test site and launchpad at Tongchang-ri "in the presence of experts from related countries." That is a site it had already promised to close, although allowing in foreign inspectors would be a step forward.
North Korea also "expressed the will to continue taking further steps like permanent dismantlement" of its main Yongbyon nuclear facility, but only if the United States takes "corresponding steps" based on Trump's agreement with Kim at their June summit.
But there wasn't enough in terms of new, concrete promises to satisfy many experts. Within Trump's own administration, senior officials want North Korea to begin by declaring its nuclear and missile sites, rather than making piecemeal, unilateral concessions. Experts also believe that North Korea has continued to build nuclear weapons this year.
"The world needs to remember that North Korea has other nuclear and missile facilities, and that these concessions will not necessarily limit or end their nuclear or missile programs," said Melissa Hanham, a senior research associate at the Middlebury Institute of International Studies at Monterey.
Hanham said North Korea made similar offers during previous rounds of negotiations, but the steps it ultimately took - demolishing a cooling tower at Yongbyon in 2008 for example - were easily reversed.
But others took a more positive view.
John Delury, a professor at Seoul's Yonsei University, argued that the two men succeeded in keeping negotiations moving forward in a process that was always going to be gradual.
Andrei Lankov, a professor at Kookmin University in Seoul, said it would take time to understand the significance of what Kim was offering, especially in relation to its Yongbyon facility, home to the country's only nuclear reactor and key to its production of weapons-grade plutonium - although other sites are believed to produce highly enriched uranium.
"If Yongbyon is actually frozen, it will not mean the end of their nuclear program. It will not even mean the end of their production of nuclear weapons. But it will be a significant decline in their ability to produce more nuclear material and nuclear weapons," he said.
Moon and Kim also agreed to several measures to ease tensions across the world's most militarized border. The measures include the establishment of a buffer zone near the front line, the suspension of artillery drills and field maneuvers there and an agreement to each pull back 11 border guard posts by year's end.
The leaders agreed to set up another buffer zone in the Yellow Sea where they would suspend maritime drills and the firing of guns, as well as a no-fly zone in border areas to prevent accidental plane clashes.
Moon again dangled the carrot of close economic cooperation, promising to reopen a joint industrial complex at Kaesong in North Korea and a tourism center at Mount Kumgang, as well as establish other special economic and tourism zones in the North "as conditions are set."
They also pledged to hold a groundbreaking ceremony this year for railways and roads to connect the two Koreas along their eastern and western coasts.
None of those economic measures will be possible unless the United Nations Security Council lifts sanctions on North Korea, however.
This article was written by Simon Denyer and Anne Gearan, reporters for The Washington Post.