SEOUL, South Korea — North Korea said Tuesday that leader Kim Jong Un supervised a test of a new rocket engine designed for intercontinental ballistic missiles, the latest step in his effort to build an arsenal that poses a viable threat to the continental United States.

North Korea’s official Korean Central News Agency said Monday’s event marked the ninth and final ground test of the solid-fuel rocket engine built with carbon fiber and capable of producing 1,971 kilonewtons of thrust, more powerful than past models. The report came a week after Kim visited the research institute that developed the engine, which North Korea then said will be used for future ICBMs, including a system called Hwasong-20.

North Korea in recent years has flight-tested a variety of ICBMs that demonstrated pote

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