SEOUL, South Korea (AP) — North Korean leader Kim Jong Un observed a test of an upgraded, high-thrust, solid-fuel engine for weapons and hailed it as a signficant development to boost the country’s strategic military capability, state media reported Sunday.

While the test was in line with Kim’s stated goal of acquiring more agile, hard-to-detect missiles targeting the United States and its allies, some experts speculate North Korea’s claim may be an exaggeration.

The Korean Central News Agency reported Kim watched the ground jet test of the engine using a composite carbon fiber material. It said the engine’s maximum trust is 2,500 kilotons, up from about 1,970 kilotons reported in a similar solid-fuel engine test in September.

KCNA reported the test was conducted as part of the country’s five-year arms build-up meant to upgrade “strategic strike means,” a term referring to nuclear-capable ballistic missiles and other weapons.

Kim said the latest engine test had “great significance in putting the country’s strategic military muscle on the highest level,” according to KCNA.

KCNA did not report exactly when or where the test occurred.

North Korea’s report on the latest test could be “bluffing” as it didn’t disclose some key information like the engine’s total combustion time, said Lee Choon Geun, an honorary research fellow at South Korea’s Science and Technology Policy Institute.

When North Korea described the September test as the ninth and final ground test of a solid-fuel engine that it earlier said would be used for intercontinental ballistic missiles. Observers predicted at the time North Korea would soon test-launch an ICBM loaded with that engine, but it hasn’t done so yet.

North Korea’s solid-fuel engine development program may be facing some delays or the country might have determined to develop a better engine, possibly with Russian technical assistence, Lee said. Cooperation between the countries has deepened in recent years, with the North sending troops and conventional weapons to support Russia’s war against Ukraine.

In recent years, North Korea has test-fired a variety of ICBMs demonstrating the potential range to reach the U.S. mainland, including missiles with solid propellants that make detection prior to liftoff more difficult. The country’s older liquid-fuel missiles must be fueled before liftoffs and cannot last long.

Some of North Korea’s past claims about major weapons test-launches drew outside skepticm. In 2024, North Korea claimed to have successfully tested a multiwarhead missile, but South Korea quickly dismissed the claim as deception to cover up a failed launch.

Some foreign experts say North Korea still faces technological hurdles before it has a functioning ICBM, such as ensuring its warheads survive the harsh conditions of atmospheric reentry. But others dispute that assessment given the number of years the country has spent on its nuclear and missile programs.

Possession of more powerful and efficient solid-fuel engines would allow North Korea to build smaller ICBMs that can be launched from submarines or land-based mobile launch trucks, Lee said. Other observers say a push to increase the engine power is likely associated with efforts to place multiple warheads on a single missile to increase chances of defeating U.S. defenses.

North Korea has pushed hard to expand its nuclear arsenal since Kim’s high-stakes diplomacy with U.S. President Donald Trump collapsed in 2019. In a ruling Workers’ Party congress in February, Kim left open the door for dialogue with Trump but urged Washington to drop demands for the North’s nuclear disarmament as a precondition for talks.

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