North Korean leader Kim Jong-un has hailed a submarine-launched ballistic missile test as an "eye-opening success", declaring that Pyongyang has the ability to strike Seoul and the United States whenever it pleases, according to the state media.
The US, joined by Britain, said Saturday's apparent test was a violation of UN Security Council resolutions and called on the North to refrain from further moves that could destabilise the region.
South Korea's defence ministry said that the launch appeared to have failed as the missile, fired from a submarine in the Sea of Japan, flew just 30km.
IN PICTURES: South Korea and US forces storm mock North Korea beach
However, the North's state-run KCNA news agency insisted that the test, which it said was personally monitored by Kim, confirmed "the reliability of the Korean-style underwater launching system".
It cited the Korean leader as saying that Pyongyang "is now capable of hitting the heads of the South Korean puppet forces and the US imperialists anytime as it pleases".
In another development on Saturday, North Korea's Foreign Minister Ri Su Yong told the Associated Press news agency in New York that his country is ready to halt nuclear tests if the US suspends its annual military exercises with South Korea. North Korea made a similar demand in January after its fourth nuclear test.
Asked if the US would consider a halt, Katina Adams, a spokeswoman for the State Department's East Asia bureau, said the exercises demonstrate the US commitment to the alliance with South Korea and enhance "combat readiness".
Pyongyang has been pushing to acquire submarine-launched ballistic missile capability that would take its nuclear strike threat to a new level, allowing deployment far beyond the Korean Peninsula and the potential to retaliate in the event of a nuclear attack.
The isolated country has conducted a number of what it says were successful missile tests, but experts question the claim, suggesting Pyongyang had gone little further than a "pop-up" test from a submerged platform.
Tension has been running high on the divided Korean Peninsula since Pyongyang's fourth nuclear test in January and rocket launch a month later, widely seen as a disguised ballistic missile test.
North Korea is banned from nuclear tests and activities that use ballistic missile technology under UN sanctions dating to 2006 and most recently adopted in March.
Pyongyang has since staged a series of short and mid-range missile tests, claiming that it had acquired significant technical breakthroughs in its nuclear strike capability.
North Korea will hold a congress of its ruling Workers' Party in early May for the first time in 36 years, at which leader Kim is expected to formally declare the country is a strong military power and a nuclear state.