"The amount of dust leads us to believe that (the explosions) were quite superficial," said an international arms official who follows North Korea closely.
According to CNN, what first appeared to be a gesture indicating North Korea might be willing to dismantle its nuclear weapons program appears to have been little more than a propaganda effort for the world's cameras.
About a week and a half ago, North Korean officials invited two dozen international journalists into the country to observe the apparent destruction of the site, billing it as an exercise in transparency. No weapons inspectors or nonproliferation experts were invited to witness the detonation.
The move was praised by many in the United States, but now initial assessments indicate that the show was essentially a charade.
"The explosions seem to have been too small" for scientists to have discerned any significant geologic activity such as collapsing tunnels, the international arms control official told CNN. "The fact that journalists were reportedly only around 500 meters from the explosions is a good indication that these were small blasts."
Preliminary analysis of North Korea's detonation indicates the explosions were not strong enough to destroy the tunnels, a US official with knowledge of the findings told CNN.
The analysis is based on seismic sensors in the region that calculated how large the explosive events were at the time.
US officials have also confirmed that imagery shows technical equipment was removed from the tunnel complex prior to the detonations, indicating the North Koreans were keeping gear for potential reuse.
Meanwhile, US Defense Secretary Jim Mattis said on Sunday that North Korea would receive relief only after it took clear and irreversible steps to end its nuclear program, adding it would be a bumpy road to a summit between US and North Korean leaders.
The comments sought to address concern the United States may be rushing to strike a breakthrough in the unprecedented summit between the two leaders after US President Donald Trump put the meeting back on track for June 12 in Singapore.
"We can anticipate, at best, a bumpy road to the (negotiations)," Mattis said at the start of a meeting with his South Korean and Japanese counterparts on the sidelines of Shangri-la dialogue in Singapore.
"We will continue to implement all UN Security Council resolutions on North Korea. North Korea will receive relief only when it demonstrates verifiable and irreversible steps to denuclearization," Mattis added.
Reuters contibuted to this report.