North Korea's latest weapons test showed it can accurately fire multiple medium-range ballistic missiles, an attack strategy that experts said could test the advanced U.S. Terminal High-Altitude Area Defense system, or THAAD, anti-missile system which began to arrive in South Korea on Tuesday.
Advances in North Korea's banned missile program have also caused concern in Tokyo, where sources with knowledge of the government's thinking said a "swarm-like" attack using multiple missiles could overwhelm Japan's already stretched defenses.
Images released by North Korean state media showed leader Kim Jong Un presiding over Monday's simultaneous launch of four ballistic missiles, which landed in seas off Japan's northwest.
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