WASHINGTON (AP) — A U.S. research institute said Thursday that North Korea has accelerated excavation at a remote mountain site that's used for underground nuclear test explosions.
Word comes from the U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies, which said the North likely started work last May on a new tunnel at the test site. It estimates that the size of the pile of earth excavated from the site has doubled so far this year.
But the institute does not see signs of an imminent test.
Findings are based on commercial satellite photographs, the latest taken Feb. 3. The analysis is being published Thursday on the institute's website, 38 North.
North Korea has conducted its three previous nuclear explosions at the site, most recently in February 2013.
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