U.S. Air Force and Special Operations aircraft have been documented as seeing heightened action in the Korean peninsula. Concern over a possible nuclear detonation test or missile test has been on the rise in North Korea following disagreements and threats, such as them promising the U.S. a “Christmas present.” This also comes three weeks after Kim Jong-un stated the country was done with a self-imposed suspension on nuclear and international ballistic missile testing. A North Korean representative to the U.N. stated that they will continue to develop more strategic weapons as long as the U.S. holds a hostile policy toward North Korea.
Source: https://www.washingtontimes.com/news/2020/jan/22/nuke-sniffer