Last week, the North said it had tested a new strategic cruise missile, implying it was designed to carry a nuclear warhead, but at the time did not mention it was being developed for submarine launch.
State media photographs published on Monday showed a missile launching into a cloudy sky from the water trailed by a plume of smoke which obscures the type of platform it was being fired from.
North Korea’s cruise missiles are typically less controversial and are not explicitly banned under UN Security Council resolutions. But analysts have said intermediate-range cruise missiles were no less a threat than ballistic missiles and are a serious capability for North Korea.
In recent months, the North has tested an array of weapons that include ballistic missile systems that are under development and an underwater drone.
Kim separately inspected the construction of a nuclear submarine and discussed issues related to the manufacturing of other types of new warships, KCNA said but gave no details.
North Korea last year launched what it called its first operational nuclear attack submarine, which analysts said appeared to be a modified from an existing submarine and likely designed to carry ballistic and cruise missiles.
There was scepticism over the real-world utility of such a vessel, especially compared to the more advanced land-based missile systems, because its diesel propulsion generates noise and is limited in range, according to weapons experts.
South Korea’s military said on Monday it believed the submarine “has no military use” and the vessel appeared to be under repair or maintenance.
Kim said at the time the country would accelerate the programme to build nuclear-powered submarines.