New satellite imagery appears to show a train of mining carts and other preparations at North Korea's nuclear test site but no indication of when a detonation might take place.
Earlier this month, South Korean intelligence reported digging of a new tunnel at the Punggye-ri site, which it took as sign that North Korea was preparing for a third nuclear test.
The U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies provided The Associated Press on Friday with its analysis of a sequence of photos of the site obtained from a private satellite operator and taken between March 8 and April 18.
The analysis estimates that 282,500 cubic feet of rubble have been excavated at the site, where nuclear tests were conducted in 2006 and 2009.
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