North Korea
North KoreaReuters

South Korea confirmed Thursday North Korea was developing solid-fuel missiles after the northern country said that it successfully test-fired one such missile. South Korea, however, said its counterpart was in the initial stages of developing such missiles.

North Korea currently uses liquid fuel for its rockets, which slows down the fuelling process, sending external agencies signals of a possible launch. Using solid fuel would quicken the launch process and leave hardly any time to detect it.

"North Korea appears to be in the (early) stages of developing solid-fuel rockets," Yonhap quoted Moon Sang-gyun, spokesman of the Ministry of National Defence, as saying during a press briefing. "North Korea's switch to solid fuel means it could do (missile) launches frequently. South Korea's military takes the move as a serious development and is preparing countermeasures."

South Korea President Park Geun-hye ordered the military Thursday to beef up security in the country after North Korea threatened to burn down the Blue House.

Geun-hye "instructed the military to be fully ready to aggressively cope with North Korea's reckless provocations," Kim Sung-woo, chief presidential press secretary, was quoted as saying by Yonhap.

North Korea's state media quoted its leader Kim Jong Un as saying Thursday the "successful" test enhanced the country's missile capability and it would be able to "mercilessly" strike its enemies, according to the Associated Press.

The United National recently levied stricter sanctions on the isolated country after it violated previous sanctions and tested nuclear and ballistic missiles. North Korea also claimed it has miniature nuclear heads.

South Korea and the U.S. jointly conducted naval exercises, following which North Korea threatened the two countries.