North Korea said Wednesday it has successfully conducted a ground jet test of a solid-fuel engine for a new type of intermediate hypersonic missile amid heightened tensions on the Korean Peninsula.

Hypersonic missiles are on the list of sophisticated weapons North Korean leader Kim Jong-un vowed to develop during a key party congress in 2021, along with nuclear-powered submarines, spy satellites and solid-fuel intercontinental ballistic missiles.

Hypersonic missiles travel at a speed of at least Mach 5 -- five times the speed of sound -- and are designed to be maneuverable on unpredictable flight paths and fly at low altitudes. At Mach 5 or higher, such a missile would be able to traverse the 195 kilometers between Pyongyang and Seoul in just one to two minutes.

Kim said that "the military strategic value of this weapon system is appreciated as important as ICBM from the security environment of our state and the operational demand of the People's Army and enemies know better about it," the Korean Central News Agency quoted Kim as saying at the Sohae Satellite Launching Ground on the country's west coast on Tuesday.

Without providing further details, the KCNA said the North was able to set a timetable for completing the development of a new hypersonic missiles weapons system with the success of the latest ground engine test.

As part of efforts to advance its weapons system, North Korea carried out ground tests of what it called newly developed solid-fuel engines for a new type of intermediate-range ballistic missile in November last year.

On Jan. 14, the North test-fired a solid-fuel IRBM tipped with a hypersonic warhead in its first ballistic missile launch this year.

South Korea's military said the latest test appeared to be aimed at making improvements to the solid-fuel IRBM launched earlier this year.

"It is suspected to be a test to improve the performance of the propulsion system of the hypersonic missile launched on Jan. 14," a Joint Chiefs of Staff official said.

Observers said the test was likely intended to extend the missile's range to target US military bases outside of the continental United States.

"It (appears) to be an attempt to increase the range to attack US military reinforcement bases, such as in Guam," Shin Jong-woo, a senior researcher at the Korea Defense and Security Forum, said, noting that the flame from the new engine test appeared to be longer than the one in November.

IRBMs have a range of up to 5,500 kilometers, putting the US base in Guam within striking distance.

The latest test came just a day after the North conducted firing drills involving super-large multiple rocket launchers, its second missile ballistic missile launch of the year. The South Korean military said Monday it detected the firing of multiple short-range ballistic missiles from areas near Pyongyang.

The North's Monday missile launch, which followed the annual Freedom Shield military exercise by Seoul and Washington, was also timed with US Secretary of State Antony Blinken's visit to Seoul. Blinken arrived in South Korea on Sunday to attend the third Summit of Democracy hosted by South Korea, a US-led multinational gathering formed to boost solidarity and shared values among democratic countries.

In January, the North's leader called for revising the country's constitution to define South Korea as its "primary foe" and codify a commitment to subjugate the South Korean territory in the event of war. (Yonhap)