North Korean state media said Wednesday that the regime had conducted successful ground-based tests of solid-fuel engines to power a new type of intermediate-range ballistic missile (IRBM).

According to Pyongyang’s state-controlled Korean Central News Agency (KCNA), the regime tested a first-stage engine on Saturday, followed by a second-stage engine on Tuesday.

“The first ground jet tests of the first- and second-stage engines were very successful and the reliability and stability of the already-established Korean-style high-thrust solid-fuel engine designing and manufacturing technologies were clearly verified once again,” the KCNA said.

Multistage missiles use two or more stages, each with its own engine and propellant, that are jettisoned when they run out of fuel, thereby decreasing the mass of the remaining missile. This process enables the thrust of the remaining stages to more easily accelerate the missile to its final speed and height.

Staging is used to both fire missiles across long distances and launch satellites into orbit.

The KCNA also said the tests “provided a sure guarantee for reliably accelerating the development of the new-type IRBM system.”

According to the state news agency, the regime’s General Missile Bureau — a North Korean agency whose existence was only made public in February — assigned “great significance” to the IRBM engine tests amid the “grave and unstable security environment” surrounding the Korean Peninsula.

Solid-fuel missiles can remain in storage for an extended period, allowing them to be deployed and launched in a shorter time frame than liquid-fuel missiles.

The North launched two Hwasong-18 intercontinental ballistic missiles (ICBM) in April and July.

Earlier this month, North designated Nov. 18 as “Missile Industry Day” to mark the anniversary of its successful test launch of the liquid-fuel Hwasong-17 ICBM last year.

The North is also in the final stage of preparations to conduct a spy satellite launch, according to South Korea’s National Intelligence Service earlier this month.

The North’s previous attempts to launch a satellite into orbit in May and August failed due to problems with second- and third-stage separation, according to both the North’s state media and outside experts.

But the NIS told lawmakers that the chances of the launch succeeding this time are higher, thanks to suspected Russian technological assistance after a rare summit between North Korean leader Kim Jong-un and Russian President Vladimir Putin in September.

The summit and subsequent agreement where the two sides said they would strengthen ties gave rise to suspicions of potential exchanges of weapons and related technologies.

The KCNA also reported Wednesday that a Russian government delegation arrived in Pyongyang the previous day for talks with North Korean officials to discuss trade and science cooperation.

The North’s solid-fuel engine tests were announced the same day that a U.S. B-52 long-range strategic bomber is set to fly over South Korea for joint air drills.

South Korean fighter jets are due to escort the B-52 bomber when it flies over South Korea, according to informed sources.

The B-52’s return to the Peninsula comes less than a month after it made its first and only landing to date in South Korea on Oct. 17.

Wednesday’s flyover marks the sixth time that joint air force drills by South Korea and the United States have involved the B-52 bomber, one of several strategic assets that Washington has deployed with greater regularity to the Korean Peninsula in response to the North’s escalating military threats.

During the allies’ bilateral security talks Monday, U.S. Secretary of Defense Lloyd Austin called the B-52’s first landing in South Korea a “milestone” in Washington’s long-standing commitment to Seoul’s defense.

He also hinted that “another carrier battle group” would soon arrive on the Peninsula.

According to the sources, the nuclear-powered aircraft carrier USS Carl Vinson is expected to dock in Busan early next week.

BY MICHAEL LEE [lee.junhyuk@joongang.co.kr]