PYONGYANG, May 20 -- The Democratic People's Republic of Korea (DPRK) has entered the phase of miniaturization and diversification of nuclear weapons for quite some time, said an official statement released Wednesday.

The news release, from the Policy Department of the National Defense Commission, referred to the May 8 test-firing of a submarine-launched ballistic missile.

The trial, it said, is an important effort to strengthen the defense capability of the country's army in line with the policy of "simultaneously developing two fronts" -- economic growth and national defense.

The launch has proved that the development of the DPRK's strategic strike means has reached a new and higher level, said the statement, adding that the country's long-range rockets are now able to ensure attacks of the highest accuracy.

The statement also blasted the United States, Japanand South Koreafor their claim that Pyongyang's test-firing of the submarine-launched ballistic missile is a threat and provocation, saying it is the DPRK's right to beef up its defense ability.

On May 9, the official KCNA news agency reported that the DPRK successfully test-fired a strategic ballistic missile from a submarine. Pyongyang said the launch fully met the requirements of latest military science and technology.

South Korean President Park Geun-hye claimed that the DPRK's development of the submarine-launched ballistic missile is a serious challenge undermining stability in East Asia as well as on the Korean Peninsula.

U.S. Secretary of State John Kerry, who had just finished a two-day visit to Seoul, said the launch was very provocative and in violation of the UN Security Council resolutions banning the DPRK from conducting any ballistic missile launches.