Satellite imagery indicates a high-level of activity at North Korea's nuclear test site to ensure the facility is always ready for use on any orders from Pyongyang, a US think-tank said.
The US-Korea Institute at Johns Hopkins University said images from July 7 of the Punggye-ri site show what appear to be supplies and/or equipment stacked next to the North Portal where the North conducted its fourth nuclear test in January.
A small vehicle was also at the nearby support building and several mine ore carts may also be present southeast of the portal, suggesting the tunnel was being actively worked.
"Based on imagery alone, it is not possible to determine whether this activity is for maintenance, excavation or preparation for a fifth nuclear test", it said Monday on its website 38 North.
"Nevertheless, it is clear that North Korea is ensuring that the facility is in a state of readiness that would allow the conduct of future nuclear tests should the order come from Pyongyang," it added.
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