Satellite photos show images dating from October and early November of the addition of a fourth tunnel at test site Punggye-ri, on North Korea’s east coast. The new tunnel is under mountains where North Korea conducts nuclear tests, and the images showed significant construction since April. While there are no indications that a nuclear test is imminent, the new tunnel adds to North Korea’s ability to conduct additional detonations at Punggye-ri over the coming years if it chooses to do so. South Korea’s Yonhap news agency quoted a South Korean government source as saying there was active movement of workers and vehicles working on a new tunnel at the site; this indicated an intention to conduct a nuclear test ‘at some point’, though this did not appear to be imminent. North Korea is under United Nations sanctions that ban trade which could fund its arms programme.