According to the North's report on Sunday, Mr. Kim watched a newly upgraded hydrogen bomb being loaded onto a new long-range missile. The bomb has explosive power that can range up to hundreds of kilotons, the North Korean report said.
Mr. Kim also specifically cited the possibility of an electromagnetic pulse, or EMP, attack. Fears of an EMP strike by North Korea have circulated for years among some U.S. policy makers, though others have openly dismissed the possibility of Pyongyang launching such a strike.
In an EMP attack, North Korea would conduct a high-altitude nuclear detonation over the continental U.S. The detonation could emit a brief but powerful electromagnetic signal capable of disrupting swaths of the U.S. electrical grid, experts say.
Ms. Hanham said while such an attack was theoretically possible, the North's goals made it more likely that Pyongyang would try to follow through on its threat to send a nuclear-tipped missile into a large American city.
