North Korea conducted the first ground tests of solid-fuel engines for a new type of intermediate-range ballistic missile last week and this week in the run-up to the country's newly-designated Missile Industry Day, the state-run Korean Central News Agency reported Wednesday.

The country's state media reported "highly satisfactory results" from the inaugural ground jet tests conducted on Nov. 11 for the first-stage engine and on Tuesday for the second-stage engine.

The two ground tests instilled further confidence in expediting the reliable development of a new IRBM, which was designated as one of the key tasks in the missile industry in North Korea's "2023 Plan for Developing Defense Science and Weapons Systems."

Experts perceive this news as part of Pyongyang's ongoing efforts to diversify solid-fuel missiles with greater mobility and survivability, including one that can hit US bases in non-contiguous territories such as Guam.

Shin Jong-woo, a senior analyst at the Korea Defense and Security Forum, noted that a new solid-fuel IRBM with a second-stage propulsion system would have an increased range compared to existing liquid-fuel IRBMs, such as the single-stage Hwasong-12, which has a range of around 3,000 kilometers.

"North Korea's pursuit to develop a solid-fuel intermediate-range ballistic missile can be interpreted as its intention to acquire capabilities to make surprise strikes on US bases in Guam, Alaska, as well as Japan," Shin told The Korea Herald.

The straight-line distance from Pyongyang to Guam is approximately 3,500 kilometers, and to Alaska, it is about 6,000 kilometers. Guam is home to strategic assets of the US military, including B-52 strategic bombers, while ground-based systems for intercepting ICBMs are stationed in Alaska.

Chang Young-keun, the director of the Missile Center at the Korea Research Institute for National Strategy, also highlighted the rationale behind North Korea's decision to conduct tests of a solid-fuel engine for a new IRBM, despite having launched the solid-fuel intercontinental ballistic missile, the Hwasong-18, in April and July this year.

North Korea has developed solid-fueled ballistic missiles such as the KN-23, KN-24, and KN-25 short-range ballistic missiles, the Pukguksong-2 medium-range ballistic missile with an approximate range of 2,000 km, and the Hwasong-18 ICBM, which underwent two lofted angle tests this year.

Notably absent from their current missile inventory is a solid-fuel IRBM with a range falling between 3,000 and 5,500 km. The existing IRBMs in North Korea's possession, including the Hwasong-12, are all liquid-fuel missiles.

Solid-fuel missiles have advantages over liquid-fueled missiles in that they can be fueled during their manufacturing process. They can also be launched on short notice.

"Therefore, it appears that North Korea is striving to develop and deploy a novel solid-fuel intermediate-range ballistic missile, prompted by the imperative need for a 3,000-km-range missile capable of targeting US military bases in Guam," Chang said. "The move shows the country's intention to diversify offensive capabilities, aiming for a strategic advantage."