PYONGYANG, North Korea: In a potential breakthrough in its efforts to acquire a more powerful, harder-to-detect weapon targeting the US, North Korea has announced that it tested a solid-fuel intercontinental ballistic missile for the first time.

The test likely represents progress in North Korea's efforts to build a nuclear arsenal that could directly threaten the US, analysts said.

Since 2027, North Korea has tested various ICBMs that could reach the US mainland, but its three previous systems cannot remain fueled for longer periods, as they used liquid fuel that must be added relatively close to launch.

In contrast, ICBMs with built-in solid propellants can be moved, hidden and fired rapidly, reducing the opportunities for their detection and counter-fire.

According to South Korea's Defense Ministry, in their their latest show of force against North Korea, US nuclear-capable B-52 bombers and South Korean warplanes flew to the Korean Peninsula for joint aerial training that was aimed at improved combined operational capabilities, including nuclear, to defend South Korea.

Meanwhile, North Korean leader Kim Jong Un pledged to increase his nuclear arsenal to "constantly strike extreme uneasiness and horror" in his rivals and "make them feel regret for their wrong choices."

The new missile would rapidly advance North Korea's nuclear response posture and further support an aggressive military strategy of maintaining "frontal confrontation" against its rivals, Kim added.

Developing solid-fuel technology will be useful for North Korea's efforts to expand its tactical nuclear arsenal and pursue submarine-based deterrents, said Leif-Eric Easley, professor at Ewha University in Seoul, according to Reuters.

In 2022, Kim announced an extensive wish list under a five-year arms development plan, which included fuel ICBMs, tactical nuclear weapons, hypersonic missiles, nuclear-powered submarines and spy satellites.