Commercial satellites have picked up fresh signs of preparations by North Korea for an expected fourth nuclear test, according to two expert image analyses.
Satellite photos taken three days ago confirm "a further increase of activity at North Korea's Punggye-ri nuclear test site, likely related to preparations for an underground nuclear test," concludes a Sunday assessment by the expert website 38 North.
38 North image analysts Nick Hansen and Jack Liu report that a number of containers and crates can be seen close to the tunnel entrances of the site's "South Portal" area. Some of these crates and boxes appeared to have been "moved into the tunnels," based on a comparison of photos dating back to April 19, the experts said.
"Of particular interest has been the rapid increase of materials near the entrance of the westernmost tunnel in the South Portal area," reads the analysis by 38 North, a project of the U.S.-Korea Institute at Johns Hopkins University. "No crates or boxes were present on April 19 but by April 25, up to nine containers can be seen near its entrance."
In a separate Friday analysis of commercial satellite photos snapped between April 23 and April 25, the Institute for Science and International Security notes the detection of possible camouflage netting over one of the South Portal tunnel entrances.
"This netting could suggest that the next test would be at this portal and North Korea is trying to shield something from view," wrote ISIS image experts David Albright and Serena Kelleher-Vergantini.
The 38 North analysts say they have yet to see any of the tunnel entrances being sealed off with concrete or dirt in preparation for an imminent atomic blast.
The website noted its prediction from last week -- that Pyongyang would not be ready to carry out a nuclear test before U.S. President Obama concluded his two-day visit to South Korea on Saturday -- has proven to be correct. By contrast, the South Korean defense ministry told reporters on Thursday that its intelligence indicated the North had placed a nuclear device and detonator in one of the tunnels and closed it off.
An important clue that a nuclear blast could be close at hand would be "an end to activity at the test site," 38 North said. "Just before the 2013 detonation, personnel, equipment and vehicles were cleared from the area, only to return a few days later."