TOKYO - North Korea claimed Thursday that it had destroyed its nuclear testing site, setting off explosions to collapse underground tunnels where it had detonated six increasingly large bombs over 11 years.
The fact that Kim Jong Un's regime went ahead with the destruction of the Punggye-ri nuclear testing site signals that it is still willing to embark on a diplomatic journey with the United States despite recent ructions.
But hours after the blasts, President Donald Trump called off a planned June 12 summit with Kim, citing "open hostility" by the North in criticizing recent U.S. comments about efforts to dismantle the North's nuclear program.
Trump noted Kim's nuclear capabilities, but emphasized the overwhelming U.S. nuclear force.
"The world, and North Korea in particular, has lost a great opportunity for lasting peace and great prosperity and wealth," Trump wrote in a letter to Kim, released by the White House. "This missed opportunity is a truly sad moment in history."
Earlier, the North set off made-for-TV blasts that were reported by journalists brought to the site. But the Kim regime did not allow any experts to observe the events, making it difficult to assess what exactly it had done. Most analysts remain highly doubtful that North Korea is really prepared to give up its nuclear program.
As both Washington and Pyongyang wrangled over the summit in recent days, the rhetoric grew more sharp on both sides. A top aide to Kim said Thursday the United States must decide whether to "meet us in a meeting room or encounter us at [a] nuclear-to-nuclear showdown."
But the regime appeared to make good on its promise to close the testing site, at least to the untrained eye. Journalists from Britain, China, Russia, South Korea and the United States reported explosions at the remote site.
"There was a huge explosion, you could feel it," said Tom Cheshire of Sky News, a British broadcaster, describing one of the detonations, which he witnessed from about 500 yards away. "Dust came at you, the heat came at you. It was extremely loud. It blew an observation tower to complete smithereens."
The reporters were unable to immediately send images because of a lack of Internet or cell access in the most inhospitable part of North Korea.
Restrictions on the journalists were tight. They set out on their 300-mile journey - involving a 12-hour train ride and then four hours on a bus, followed by an hour hiking through the mountains. A Russian journalist reported that the window blinds on the train were secured so they couldn't see out.
North Korea's Nuclear Weapons Institute declared Thursday night that the site was no longer usable.
"Dismantling the nuclear test ground was done in such a way as to make all the tunnels of the test ground collapse by explosion and completely close the tunnel entrances," a deputy director at the institute said, according to state media.
No radiation leaked from the site and the explosions did not cause any environmental damage, it said, statements that could not be independently verified. The journalists had their dosimeters confiscated so they couldn't check for radiation.
The Punggye-ri testing site consisted of a series of tunnels under the mountains in the northeast of the country, which were accessed through four portals.
The first tunnel to be blown up was through the north portal, the location of the last five nuclear tests. The most recent test, conducted in September, was widely considered to have been a hydrogen explosion.
Since that test, there have been suggestions that Mount Mantap might be suffering from "tired mountain syndrome," and many experts say that the north portal tunnels are now unusable.
Those tunnels were destroyed with dynamite at about 11 a.m. local time, according to South Korean pool reports from the scene.
However, the west and south portals had never been used and experts said they were still considered viable for future tests. The west portal was blown up shortly after 2 p.m., and the southern one at 4 p.m. Then barracks, observation towers and other buildings were destroyed, according to the reports.
The east portal, through which North Korea conducted its first nuclear test, in 2006, has been abandoned for more than a decade and is no longer accessible.
There remains a considerable amount of skepticism about Thursday's events, given that North Korea invited foreign media to film the spectacular destruction of the cooling tower at the Yongbyon nuclear plant in 2008, part of a denuclearization deal that was meant to cut off North Korea's access to plutonium.
The images looked impressive at the time - then it transpired a couple of years later that North Korea had been building a huge uranium enrichment facility all the while, giving it another source of fissile material.
Still, despite the shortcomings of Thursday's ceremony, analysts said it was a move in the right direction, even if it was little more than a gesture.
"This will be highly symbolic and a diplomatic first step," said Frank Pabian, a former nuclear nonproliferation and satellite imagery expert at the Los Alamos National Laboratory. "But in and of itself, it won't change anything about North Korea's nuclear capabilities."
Although no nuclear experts were allowed to attend the event, Pabian, who now writes for the specialist website 38 North, said that officials from organizations like the Comprehensive Test Ban Treaty Organization would still be able to carry out testing if they were ever granted access to the site.
North Korea has signaled it no longer needs to test its nuclear devices because it has mastered the technology, a claim that is not without credibility given its quantifiable advances over 11 years of testing.
The last nuclear test caused a 6.3-magnitude earthquake at the site and had a yield of as much as 250 kilotons. The American nuclear bomb detonated over Hiroshima in 1945 had a yield of about 15 kilotons of energy.
North Korean called that test a "perfect success" and said it had done all the testing needed. Kim reiterated the message last month at a Workers' Party meeting in Pyongyang, the North Korean capital.
"The mission of the northern nuclear test ground has thus come to an end," Kim told his top cadres. By acquiring this "powerful treasured sword for defending peace," North Koreans could now "enjoy the most dignified and happiest life in the world," he said.
North Korea's Foreign Ministry confirmed May 12 that the site would be "completely closed."
This came after a historic summit with South Korean President Moon Jae-in late last month, where Kim agreed to embark on a number of steps to show he was serious about dealing with the United States, the North's avowed enemy.
He also mentioned a plan to work toward "the complete denuclearization of the Korean Peninsula" - a phrase that Trump took to mean Kim wanted to give up his weapons, while most analysts said it was code for a drawn-out process under which both sides would have to make concessions.
In an interview broadcast Thursday before officially canceling the summit, Trump said the United States might accept a "phase-in" of North Korea's denuclearization, but insisted the dismantling of the nuclear program must progress "rapidly."
"We're going to see. I'd like to have it done immediately," Trump said on "Fox & Friends" on Fox News. "But, you know, physically, a phase-in may be a little bit necessary, we will have to do a rapid phase in, but I'd like to see it done at one time."
The two sides appeared to being using a "willingness to walk" from the summit as a source of leverage, said Katrin Katz, a North Korea expert at Northwestern University.
"Thanks to the North Koreans' rhetorical pivot, both sides are now in a competition to seem the least desperate to meet - and to place the blame for not meeting on the other side," she said.
"This type of behavior contrasts with North Korea's recent charm offensive but not its longer term behavior," she said, noting that it could have a positive effect: it could give an American president who likes to "wing it" more time to come up with a careful plan.