According to 38 North, the imagery shows several key operational support buildings have been razed, and that some of the rails for mining carts - which had led from the tunnels to their respective spoil piles - have apparently been removed.
North Korean state media reported over the weekend that the country had scheduled the dismantlement of its nuclear bomb site for later in May.
The respected 38 North website said Tuesday that satellite images dated May 7 showed "the first definitive evidence that dismantlement of the test site was already well under way".
"The Nuclear Weapon Institute and other concerned institutions are taking technical measures for dismantling the northern nuclear test ground.in order to ensure transparency of discontinuance of the nuclear test", KCNA said.
Pompeo met previously with Kim while Central Intelligence Agency director, flying secretly to North Korea over the Easter weekend to discuss the possibility of a summit meeting with Trump and negotiations over North Korea's nuclear program. Chinese geologists claimed in a study the cavity caused by last September's nuclear test collapsed shortly after the detonation, causing a powerful tremor.
However, analysts say the last five nuclear tests were all conducted using the same tunnel, and that although that tunnel may be damaged beyond fix, the North Koreans could dig others for potential future tests.
Pompeo: US Willing to Aid North Korea's Economy for Denuclearization
He'd said he favored holding the meeting at the Demilitarized Zone, the heavily fortified border separating the Koreas. Both Trump and Kim have set " denuclearization of the Korean Peninsula " as the goal of the summit.
Pompeo cast US President Donald Trump's June 12 summit with Kim Jong Un as a test of the North Korean leader's commitment to change his country's direction.
"If North Korea takes bold action to quickly denuclearize, the United States is prepared to work with North Korea to achieve prosperity on the par with our South Korean friends", he said Friday. "What we need to see from Kim Jong Un is that he and the entire North Korean regime have made a strategic decision that they'll be better off without weapons of mass destruction".
North Korea, which is believed to manage a vast subterranean network in part to frustrate USA and South Korean spies and military planners, probably has other locations that could house tests.
According to a report from Voice of America on Monday, a White House official said while Washington welcomed Pyongyang's decision to close down the nuclear site, the process should undergo inspections by global experts.
Last month, Pompeo became the first known United States official to meet with Kim, where he helped lay the groundwork for the upcoming meeting with Trump.
"The returnees have been reunited with their families".