South Korea confirmed Thursday that North Korea is developing solid-fuel rockets, which would allow the country to conduct rocket launches "frequently."

"North Korea appears to be in the (early) stages of developing solid-fuel rockets," Moon Sang-gyun, spokesman of the Ministry of National Defense, said during a press briefing.

"North Korea's switch to solid fuel means it could do (missile) launches frequently," the spokesman said.

South Korea's military takes the move as a serious development and is preparing countermeasures, he said.

The North's state-run Korean Central News Agency reported earlier in the day it has successfully conducted a test of a solid-fuel rocket engine.

It flaunted the test as an accomplishment that will boost its ballistic missile capabilities to hit enemies.

The success of this test will "strike great horror and terror into the hearts of the enemies," leader Kim Jong-un said during the test.

Commenting on the claimed success, Moon said the North Korean report seems to try to show off the progress the country has supposedly made in its nuclear and missile programs.

Over the past weeks, North Korea claimed it has attained nuclear warheads and missile re-entry technology, a sophisticated tech that deals with resisting the immense heat and pressure that a ballistic missile sustains when it re-enters the earth's atmosphere from outer space.

Currently, North Korea relies on liquid fuel to propel most of its ranged ballistic missiles, including the short-range Scud, mid-range Rodong and the KN-08 intercontinental ballistic missiles.

Conventionally, using liquid fuel means that fueling a rocket takes longer, allowing the outside world more time to detect an imminent launch and predict its timeframe.

Solid propellant helps reduce the time that the fueling stage takes, thus significantly reducing the chance of launch preparations being noticed by outside surveillance.

With the claimed success of the solid fuel engine, North Korea is likely to quicken steps to replace its currently liquid-fuel rockets with solid propellant-based ones.

Still, it may take a long while for North Korea to complete the development of solid-fuel intercontinental ballistic missiles, experts said.

"It is possible for the Scud and Rodong missiles to have solid rocket fuel, but it may take time for it to be used on the KN-08,"

Lee Chun-geun, a researcher at the Science and Technology Policy Institute, said. (Yonhap)