North Korean dictator Kim Jong Un oversaw a test of a new high-thrust solid-fuel rocket engine, according to state media, working on weapons capable of striking the U.S. mainland.

The test, reported Sunday by KCNA, involved an engine made with carbon-fiber materials and was described as part of a new five-year defense plan to upgrade the country’s "strategic strike" capabilities.

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

The engine reportedly produced 2,500 kilonewtons of thrust, higher than a similar engine it tested last year. Analysts say such engines could support more mobile or compact long-range missiles.

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North Korea’s report on the latest test could be "bluffing" as it did not 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.

Solid-fuel systems are significant because they can be launched more quickly and with less warning than older liquid-fuel missiles, making them harder to detect and potentially more survivable in combat.

Pyongyang still faces major technical barriers before fielding a fully reliable intercontinental ballistic missile, especially ensuring a warhead can survive atmospheric reentry.

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Kim’s latest military activities also included inspections of special operations training and tests of a new main battle tank, underscoring a broader push to modernize both North Korea’s missile program and conventional forces, according to KCNA.

Kim claimed the tank’s protection system could defeat nearly all existing anti-tank weapons, though such assertions could not be independently verified, Reuters reported.

The developments fit a wider pattern of stepped-up military activity by Pyongyang. Since the collapse of Kim’s diplomacy with President Donald Trump in 2019, North Korea has accelerated work on nuclear and missile systems despite sanctions, while keeping open the possibility of talks if Washington drops demands for denuclearization first.

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At a rare ruling party congress held in February, Kim unveiled a new five-year plan that reaffirmed continued development of nuclear weapons, while calling for a broad upgrade of the country’s military capabilities.

Analysts and regional governments also pointed to new tank and combined-arms drills as part of Pyongyang’s effort to adapt its military doctrine to modern warfare, drawing lessons from recent conflicts and emphasizing integration across ground and missile forces.

South Korea and the United States say they are closely monitoring North Korea’s weapons developments.

The Associated Press and Reuters contributed to this report.