PANMUNJOM, Demilitarized Zone — With his bed less than 50 feet from the North Korean border, Maj. Luca Meli jokes that he sleeps closer to the reclusive nuclear-armed state than anyone in the world. 

From his bedroom in the heavily fortified buffer zone that separates North and South Korea, the Swiss soldier has a front-row view of the North’s expanding military activities amid the highest tensions on the Korean Peninsula in years. 

“We hear explosions every night,” he said.

As a…