Earlier this month, a resident in a rural province of South Korea found a small, sky-blue unmanned plane perched nose-up against a tree in a remote forest.
The drone belonged to the North Korean military and apparently had flown south for five hours, capturing images of a sensitive new U.S. anti-missile system before crashing.
It lacked missiles or other weapons like the larger, more advanced models used by U.S. forces in the Middle East. But South Korean officials and security experts consider such flights unlawful incursions.
“It’s a military provocation. It’s an agent spying on a neighboring country’s military information,” Kim Dong-Yub, a professor...