Since nuclear explosion
s are famed not only for their destructive potential but also for the huge amounts of electromagnetic radiation
they chuck around, I believe that any sort of nuclear explosion would have been detected immediately after the event. The US
designed for the purpose of spotting nuclear launches and explosions, and I'm sure that the U.S. Government
would not hide the fact that a nuclear explosion had occurred in a friendly country for long.
Plus, the EM
pulse would be detectable thousands of miles