BEIJING—The damage to the nuclear test site that North Korean leader Kim Jong Un has promised to shut down is more extensive than earlier assessments showed, according to a new study by a team of international scientists. 
 
 Space-based radar showed that after the initial impact of North Korea’s latest nuclear test in September last year, a much larger part of the Punggye-ri test site caved in over the following hours and days, according to a study published in Science magazine on Thursday. The study was conducted by researchers from Singapore, Germany, China and the U.S. 
 
 “This means that a very large domain has collapsed around the test site, not merely a tunnel or two,” said Sylvain Barbot, one of the authors who is an assistant professor at Nanyang Technological University in Singapore. 
 
 RUSSIA CHINA Shenyang Punggye-ri nuclear test site NORTH KOREA Pyongyang Sea of Japan (East Sea) Seoul SOUTH KOREA Busan 100 miles JAPAN 100 km 
 
 The research feeds into an international debate over the value of Mr. Kim’s commitment to close the test site in the run-up to last month’s inter-Korean summit and his meeting with President Donald Trump, expected this month or early next. 
 
 Some U.S. officials and experts see the closure as a significant concession while others argue that the site is unusable and its dismantling is therefore an empty gesture designed to gain leverage in negotiations with Seoul and Washington. 
 
 Chinese seismologists involved in a study published last month concluded that a large part of the site was unusable due to the collapse of a cavity inside a mountain there, Mount Mantap, a few minutes after the last test. 
 
 U.S. researchers studying satellite imagery have since argued that, while tunnels may be severely damaged under Mount Mantap—where five of North Korea’s six nuclear tests took place—other parts of the Punggye-ri site are still usable. 
 
 Related Video President Donald Trump and North Korean leader Kim Jong Un both say they want denuclearization, but they may have different definitions of the word. WSJ's Shelby Holliday explains. 
 
 Mr. Kim told South Korean President Moon Jae-in at their summit that two bigger tunnels at the site were still in good condition, according to Seoul’s presidential Blue House. 
 
 The last test caused an initial magnitude-6.3 earthquake, followed by a smaller tremor 8½ minutes later that was triggered by the collapse of damaged rock above the blast cavity, the Chinese study said. 
 
 The new study, which created three-dimensional images of the site, backs the Chinese researchers’ conclusion that a large part of the site can’t be used—while showing that the initial damage is “dwarfed” by the gradual collapse detected from space over the next few hours and days. That damage covers an area with a radius of 800 meters and a height of 400 meters, according to Mr. Barbot, who is also an adjunct professor at the University of Southern California. 
 
 “These findings make us infer that a large part of the Punggye-ri test site is inoperable and that further test may require a substantial investment in the construction of another facility elsewhere,” he said. 
 
 Write to Jeremy Page at jeremy.page@wsj.com ||||| FILE - This Wednesday, May 23, 2018 satellite file image provided by DigitalGlobe, shows the Punggye-ri test site in North Korea. North Korea has carried out what it says is the demolition of its nuclear... (Associated Press) 
 
 PUNGGYE-RI, North Korea (AP) — North Korea carried out what it said is the demolition of its nuclear test site Thursday, setting off a series of explosions over several hours in the presence of foreign journalists. 
 
 The explosions at the nuclear test site deep in the mountains of the North's sparsely populated northeast were centered on three tunnels into the underground site and a number of observation towers in the surrounding area. 
 
 The planned closing was previously announced by leader Kim Jong Un ahead of his planned summit with U.S. President Donald Trump next month. 
 
 The North's decision to close the Punggye-ri nuclear test site has generally been seen as a welcome gesture by Kim to set a positive tone ahead of the summit. Even so, it is not an irreversible move and would need to be followed by many more significant measures to meet Trump's demands for real denuclearization. 
 
 By bringing in the foreign media, mainly television networks, the North is apparently hoping to have images of the closing — including explosions to collapse tunnel entrances — broadcast around the world. The group included an Associated Press Television crew. 
 
 The North did not invite international inspectors to the ceremony, which limits its value as a serious concession. ||||| Several key operational buildings as well as smaller sheds have been razed, according to a US monitoring group 
 
 North Korea has begun dismantling the country’s only known nuclear test site, according to satellite photos, following through on a promise made by leader Kim Jong-un ahead of his meeting with Donald Trump. 
 
 
 
 The pictures, taken on 7 May, are “the first definitive evidence that dismantlement of the test site was already well underway”, according to a blog post by 38 North, a website run by former US diplomats. 
 
 The Punggye-ri site in the northeast of the country was used for all of the North’s six nuclear tests and lies deep within mountains. Kim pledged to close the complex after his historic meeting with South Korean president Moon Jae-in, saying North Korea no longer needed the site. 
 
 There were reports the site had collapsed and was unusable, but Kim himself reportedly dismissed those claims, saying “we have two more tunnels that are bigger than the existing ones and that they are in good condition”. North Korea has said it will dismantle its nuclear bomb test site later this month in order to uphold its pledge to cease tests. 
 
 The two countries will hold high-level talks on Wednesday to discuss steps needed to uphold the pledge to denuclearise the Korean peninsula and formally end the Korean War. 
 
 The new images show key buildings and several smaller sheds have been torn down and a rail line connecting one of the entrances had been removed. Excavation of a new tunnel appears to have stopped in March. 
 
 “This activity along with the rail removal could be further evidence of an operational shut down,” according to 38 North. 
 
 North Korea’s plan to close the site has been welcomed by Washington, Seoul and the UN secretary general. 
 
 “I would imagine that the plan is to sanitize the site to remove any sensitive information about the state of North Korea’s nuclear weapons development, then invite in the journalists and experts to confirm that, yes, the site is now a ghost-town,” Jeffrey Lewis and David Schmerler, both arms control experts, wrote in a separate blog post analysis satellite imagery. 
 
 
 
 North Korea’s release of US prisoners doesn’t mean peace | Polly Toynbee Read more 
 
 North Korea’s foreign ministry has said it will invite foreign journalist to witness the decommissioning of the site at Punggye-ri. One new structure could be a camera position to record the closure of the West Portal, 38 North said. 
 
 “Dismantlement of the nuclear test ground will be done in the following sequence-making all tunnels of the test ground collapse by explosion; completely blocking entries; removing all observation facilities, research institutes and structures of guard units on the ground,” the ministry said in a statement released through the state run Korean Central News Agency. 
 
 Dialogue brokered by South Korea has seen US-North Korea relations go from trading personal insults and threats of war last year to a summit between Kim and Trump which will be held in Singapore on 12 June. 
 
 
 
 Washington is seeking the “complete, verifiable and irreversible denuclearisation” of the North and stresses that verification will be key. 
 
 But sceptics warn that Pyongyang has yet to make any public commitment to give up its arsenal, which includes missiles capable of reaching the United States.
– The nuclear test site that Kim Jong Un promises to shutter may be in worse shape than the world knew, the Wall Street Journal reports. The Punggye-ri site—which is couched in a mountain called Mount Mantap—apparently suffered a sizeable collapse in the hours and days after North Korea's most recent nuclear test in September. An international team of scientists reached this conclusion by combining seismic data with satellite radar images, Nature reports. "These findings make us infer that a large part of the Punggye-ri test site is inoperable," says a USC professor. Seismologists have already shown that a big part of the site was unusable after the last test caused a near-immediate collapse of a cavity in Mount Mantap. The latest study used synthetic aperture radar—which is normally used to make 3D terrain maps—to show that Mantap's slopes moved outward horizontally by nearly four yards, and the summit sank by about half a yard over the next week when "damaged rock above the cavity slowly settled in on itself," says Nature. The latest finding may add to concerns that Kim's plan to close Punggye-ri before meeting President Trump isn't much of a concession. North Korea said Saturday that it plans to dismantle Punggye-ri on May 23-25, the AP reports.