New commercial satellite imagery has provided the first definitive evidence that North Korea is dismantling its Punggye-ri nuclear test site ahead of a scheduled ceremony next week to mark the event, USA researchers said Monday.
Some of the rails for mining carts have also apparently been removed, the website said, adding that some carts seem to have been tipped over or disassembled.
The site has been used for each of its six underground nuclear test explosions.
But both countries have been on charm offensives ahead of the summit June 12 in Singapore between Donald Trump and Kim Jong Un, the first ever between a sitting United States president and a North Korean leader.
Experts say that it is still a meaningful step toward denuclearization ahead of its unprecedented summit talks, to be held on June 12 with the USA, where its nuclear weapons program will likely top the agenda.
Bolton said the U.S. side also will discuss not just North Korea's nuclear and missile programs but its chemical and biological weapons arsenal as well.
Journalists from countries including South Korea, China, Russia, the United Kingdom, and the USA are expected to attend the decommissioning ceremony and will take a charter flight from Beijing to the resort town of Wonsan.
Secretary of State Mike Pompeo says that North Korea will receive sanctions relief should they follow through with total denuclearization of the Korean Peninsula. "I think what the prospect for North Korea is to become a normal nation, to behave and interact with the rest of the world the way South Korea does".
"It's nothing but a show to destroy evidence of previous nuclear tests", said Chun Young-woo, former national security adviser for conservative President Lee Myung-bak.
While South Korea's government appeared to downplay the absence of nuclear experts and global watchdogs, the U.S. and Japan stressed the need to invite them for a more verifiable process.
Kim has declared the development of the North's nuclear force complete and that it had no further need for the site.
North Korea's foreign ministry has said it will invite foreign journalist to witness the decommissioning of the site at Punggye-ri.
Mr Kim had already revealed plans to shut the test site by the end of May during his summit with South Korean President Moon Jae-in last month.
Some experts believe Kim may try to drag out the process or seek a deal in which he gives away his intercontinental ballistic missiles but retains some of his shorter-range arsenal in return for a reduced USA military presence in the South.
'Make no mistake about it, America's interest here is preventing the risk that North Korea will launch a nuclear weapon into L.A. or Denver or to the very place we're sitting here this morning, ' Pompeo said from Washington.