North Korea has dug a new 800 m-deep tunnel at its nuclear test site in Punggye-ri, North Hamgyong Province, it emerged on Sunday. Experts believe it will be ready for another nuclear test once it reaches a depth of 1 km. A South Korean government source said, "If they continue digging the tunnel in Punggye-ri at the current speed, they could likely conduct a third nuclear test anytime after early April."
The tunnel had reached a depth of about 500 m by December. South Korean and U.S. intelligence agencies estimate progress based on satellite images of mounds of soil dug from the tunnel.