Developing advanced solid-fuel missiles — which are quicker to launch and harder to detect and destroy in advance — has long been a goal for North Korean leader Kim Jong Un.
A missile launched by North Korea on Thursday flew higher and stayed in the air for a longer duration than any other weapon the country had so far fired.
North Korea test-fired a suspected intercontinental ballistic missile that could strike the United States.
Kim vowed to bolster his nuclear weapons after accusing the US and South Korea of threats.