The United States, South Korea and Japan conducted a joint missile defense exercise Monday in waters near the Korean Peninsula as they expand military training to counter the growing threats of North Korea’s nuclear-capable missiles.

Last week, North Korea conducted one of its most provocative weapons demonstrations in years by flight-testing for the first time an intercontinental ballistic missile powered by solid propellants, as it pursues a weapon that’s more responsive, harder to detect and could directly target the continental United States.