The "undeclared" base Sinpung-Dong is located just under three miles from China, according to the American think tank Center for Strategic and International Studies (CSIS) in a report.
The facility likely houses six to nine intercontinental ballistic missiles, so-called ICBM, according to the study.
The weapons "constitute a potential nuclear threat to East Asia and the US mainland", the authors write.
North Korea has stepped up its nuclear program since a failed summit with US President Donald Trump in 2019, during his first term. Since Russia's invasion of Ukraine in 2022, Pyongyang has instead tied closer links with Moscow.
According to CSIS, North Korea has a total of 15-20 military bases for storage and maintenance of ballistic missiles and warheads. Dictator Kim Jong-Un recently urged a "rapid expansion" of the isolated country's nuclear capacity.
