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There are new indications that North Korea may be transferring nuclear weapons technology to Myanmar, the dictatorship also known as Burma, and that it earlier supplied a reactor to Syria. For many years, based on five visits to North Korea and its border areas, I’ve argued for an “engagement” approach toward Pyongyang, but now I’ve reluctantly concluded that we need more sticks.

Burmese defectors have provided detailed accounts of a North Korean reactor, perhaps a mirror of the one provided to Syria, built inside a mountain deep in Myanmar. The reports, first aired in The Sydney Morning Herald this month, come from Desmond Ball, a respected Asia scholar, and Phil Thornton, a journalist with expertise on Myanmar, and there has been other fragmentary...