Photos from a return visit by Mr. Kim last August showed CNC machines with bright orange, robotic arms bearing the logo of Swiss engineering company ABB Ltd.

Weapons experts who study satellite images and photos released by North Korea say the newer machines have become ubiquitous in North Korean missile plants. The machines allow faster, more precise manufacturing of parts around the clock, reducing the need to skirt sanctions by importing similar parts. The United Nations bans any imports that could be used in weapons programs.

Weaponry in a military parade in April in Pyongyang to mark the 105th anniversary of the birth of state founder Kim Il Sung, the grandfather of Mr. Kim, included rocket casings that might have been made by the new CNC machines, missile experts say. North Korea also showed off what appeared to be at least one new long-range missile.