A hypersonic missile is among the high-tech weapons systems that North Korean leader Kim Jong Un vowed to introduce to cope with what he called deepening U.S. hostility.

North Korea successfully tested a solid-fuel engine for its new-type intermediate-range hypersonic missile, state media reported Wednesday, claiming progress in efforts to develop a more powerful, agile missile designed to strike faraway U.S. targets in the region.

A hypersonic missile is among an array of high-tech weapons systems that North Korean leader Kim Jong Un publicly vowed to introduce in 2021 to cope with what he called deepening U.S. hostility. Outside experts say Kim wants a modernized weapons arsenal to wrest U.S. concessions like sanctions relief when diplomacy resumes.

On Tuesday, Kim guided the ground jet test of the multi-stage solid-fuel engine for the hypersonic missile at the North’s northwestern rocket launch facility, the official Korean Central News Agency reported.