SEOUL - North Korea said on Sunday it had conducted a submarine-launched ballistic missile test supervised by leader Kim Jong Un and it was a "great success" that gave the country "one more means for powerful nuclear attack."North Korea fired one missile from a submarine off its east coast on Saturday, South Korea's military said, amid concerns that the isolated state might conduct a nuclear test or a missile launch ahead of a rare ruling party meeting in May.The missile flew for about 30 km (18 miles), a South Korean Defence Ministry official said late on Saturday, adding its military was trying to determine whether the launch may have been a failure for unspecified reasons.But the North's official news agency KCNA said an underwater test-fire of a ballistic missile was "another great success," without disclosing the date and place of the event which was guided by leader Kim."It fully confirmed and reinforced the reliability of the Korean-style underwater launching system and perfectly met all technical requirements for carrying out ... underwater attack operation," KCNA said."The successful test-fire would help remarkably bolster the underwater operational capability of the KPA navy, he said, adding that it is now capable of hitting the heads of the South Korean puppet forces and the US imperialists anytime as it pleases," it said, quoting Kim. KPA refers to the North's military.The US Strategic Command said on Saturday it had detected and tracked a North Korean submarine missile launch but it did not pose a threat to North America. State Department spokesman John Kirby said launches using ballistic missile technology were "a clear violation of multiple UN Security Council resolutions."France on Saturday called on the European Union to unilaterally adopt additional sanctions on North Korea if the missile launch was confirmed.North Korea first attempted a launch of the submarine-based missile last year and was seen to be in the early stages of developing such a weapons system, which could pose a new threat to its neighbors and the United States if it is perfected.