The researchers are relying on commercial satellite imagery from May 7, according to the 38 North web site.
Punggye-ri, in the northeast of the country, has been the site of all six of the North's nuclear tests, the latest and by far the most powerful in September previous year, which Pyongyang said was an H-bomb.
North Korea said on Saturday that it will dismantle its northeastern Punggye-ri test site between May 23 and 25 in the presence global media.
Punggye-ri, in the northeast of the country, has been the site of all six of the North's nuclear tests.
Limits on foreign journalists were due to space constraints, it said, as the site was in an "uninhabited deep mountain area".
The shutdown process will unfold under the presences of journalists, including those from the US and South Korea.
The eight South Korean journalists - four each from a wire agency and a broadcaster that have yet to be determined - will take a chartered flight from Beijing to the North Korean coastal town of Wonsan on May 22, the ministry said. After a half dozens tests over a period of more than a decade, some experts believe that Pyongyang is far enough along in its nuclear weapons development that it no longer has to detonate bombs underground to move its program along.
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After their April 27 meeting, Kim and Moon issued a vague vow for the "complete" denuclearization of the Korean Peninsula.
Bolton pointed out that signing off on "the complete ending of the nuclear program in one day" is not likely, but added that the United States is "very much interested in operationalizing the commitment as quickly as possible - and that is in North Korea's interest". The "subcritical" experiments give scientists an opportunity to test weapons without causing an actual nuclear chain reaction and explosion.
Trump and North Korean leader Kim Jong Un are set to meet June 12 in Singapore for the first ever summit between a sitting US president and a North Korean leader. Trump welcomed the "gracious gesture".
The North's announcement comes days after Washington announced that the historic summit between Mr Kim and Mr Trump will be held on June 12 in Singapore.
North and South Korean leaders were scheduled to meet for crucial talks on Wednesday in the city of Panmunjom, South Korea.
"It's a game changer in terms of the diplomacy, certainly".
"I think they're done testing. The downside is if it fails then we've hit the diplomatic cliff and could fall off the other side".
The head of the UN's World Food Programme said Saturday it appeared North Korea was "turning a new page in history", following a four-day visit to the country. In 2008, global journalists looked on as a water cooling tower at a facility called Yongbyon was destroyed.