A U.S. military satellite has observed developments at the North Korean Punggye-ri nuclear test site that constitute “imminent signs” of a coming nuclear test, a senior Pentagon official has told American news network CNN.

The satellite images were reported to show one of the tunnel entrances covered by a tarpaulin, typically used to hide the delivery of equipment or indeed a nuclear device to the underground system in preparation for a test.

Similar developments occurred immediately prior to North Korea’s third and most recent nuclear test on February 13, 2013 when satellites observed tarpaulins covering the tunnel entrances at the same