CNN reported a tarp has been set up at the tunnel entrance of North Korea's nuclear test site in Punggye-ri, North Hamgyeong Province.
 
The news agency reported a senior U.S. official said a U.S. spy satellite flying over North Korea late last week spotted a tarp over a tunnel entrance at the nuclear test site.
 
CNN said putting up a tarp implies the North does not want U.S. satellites to see what it is doing. It said closing off the tunnel entrance would be one of the final steps before the North actually initiates an underground nuclear explosion.

South Korean intelligence authorities say North Korea is intentionally exposing its activities in the test site as they prepare for a fourth nuclear test. They say there is a possibility the North is engaging in delay tactics to confuse Seoul and Washington’s intelligence authorities.