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, U.S. researchers said Monday.

The North Korea-watching 38 North website said in a report that imagery from May 7 showed that the process was “already well under way” at the site, which has been used for each of the North’s six underground nuclear test explosions.

It said several key operational support buildings, located just outside the north, west and south tunnel portals, had been razed, while some of the rails for mining carts, which had led from the tunnels to their respective spoil piles, had apparently been removed.

Additionally, it said, some carts appeared to have been tipped over or disassembled, and several small sheds or outbuildings around the site removed.

Still, the report said, other more substantial buildings around the facility remained intact, including the two largest buildings at the command center, and the main administrative support area.

The website also said a small square-shaped foundation and a small shed had been newly placed on the north portal spoil pile. It said that while it is too early to determine their intended purpose, “it is conceivably for a future camera position to record the closure of the west portal.”

It also said that “no tunnel entrances appear to have yet been permanently closed.”

“This may be because on May 12, the official Korean Central News Agency (KCNA) announced that the final dismantlement of the Punggye-ri nuclear test ground would be witnessed by foreign journalists and would involve the ‘collapsing all of its tunnels with explosions, blocking its entrances, and removing all observation facilities, research buildings and security posts,’ ” 38 North said.

The North Korean announcement said the ceremony would take place between May 23 and 25, weather permitting.