An undated photo shows the scene of North Korea firing a submarine-launched ballistic missile. [Photo: weibo.com]

PYONGYANG, Aug. 25 -- Top leader of the Democratic People's Republic of Korea (DPRK) Kim Jong Un has recently guided a successful test-firing of a strategic submarine-launched ballistic missile "Pukguksong", the official news agency KCNA reported Thursday.

The test-firing, which was conducted at a high angle in the maximum launching depth, reconfirmed the stability of the SLBM (submarine-launched ballistic missile) system, the starting character of the high-power solid fuel engine and phased flying kinetic feature, the state media said.

"The core technical indexes of the ballistic missile including the reliability of the phased heat separation and the control and guidance system and the working accuracy of the warhead in the re-entry section perfectly met all requirements for operation," it added.

Kim was satisfied with the result and expressed gratitude to the officials, scientists and technicians in national defense and munitions factories for their efforts to develop the SLBM technology.

Kim said the test-firing has proved the DPRK "joined the front rack of the military powers fully equipped with nuclear attack capability" and that the U.S. mainland and military bases in the Asia Pacific are now within the striking range of the DPRK's military.

The supreme leader strongly slammed the ongoing military drills jointly carried out by South Korea and the Untied States and threatened to "deal merciless blows with nuclear hammers," once an opportunity is given.

He also stressed the need to speed up mounting nuclear warheads on ballistic missiles and to focus efforts on the development of the delivery means.

The DPRK test-fired a submarine-launched ballistic missile at about 5:30 a.m. local time (2030 GMT Tuesday) off the eastern coastal town of Sinpo in South Hamgyeong province, according to South Korean defense ministry.

The ballistic missile flew about 500 km and fell into the waters inside Japan's Air Defense Identification Zone, or ADIZ, said South Korean local media. Japan's Prime Minister Shinzo Abe described the launch as a grave threat to security and said Japan has lodged strong protest through diplomatic channels.

Seoul believed the DPRK's SLBM technology has progressed compared with previous launches as the military has allegedly regarded the flight of more than 300 km as successful.

The launch came just two days after Seoul and Washington kicked off their joint annual war games, codenamed Ulchi Freedom Guardian (UFG). Pyongyang has denounced the drills as a dress rehearsal for northward invasion, which the two allies claimed to be defensive in nature.

The previous SLBM test by the DPRK came just a day after Washington and Seoul announced on July 8 the decision to deploy a Terminal High Altitude Area Defense (THAAD) missile defense system in South Korea.

Experts are worried that the THAAD deployment may accelerate the DPRK's efforts to develop its SLBM technology as THAAD's X-band radar cannot detect and track ballistic missiles fired from a DPRK submarine that moves deep under the waters.