The two Pulhwasal-3-31 missiles "flew in the sky above the East Sea... to hit the island target" on Sunday, state-run news agency KCNA reported, adding that Kim Jong Un had "guided" the launch.

The Pulhwasal-3-31 is a new generation of strategic cruise missile that Pyongyang said it had only tested for the first time on Wednesday, firing multiple missiles toward the Yellow Sea.

Sunday's test from the submarine "had no impact on the security of a neighboring country and has nothing to do with the regional situation," the report continued, adding that Kim had "expressed great satisfaction" with the launch.

South Korea's military said Sunday that it had detected cruise missiles fired near waters around the North's Sinpo area.

Pyongyang has accelerated weapons testing in the new year, including tests of what it called an "underwater nuclear weapon system" and a solid-fuelled hypersonic ballistic missile.

Unlike their ballistic counterparts, the testing of cruise missiles is not banned under current UN sanctions against Pyongyang.

Cruise missiles tend to be jet-propelled and fly at a lower altitude than more sophisticated ballistic missiles, making them harder to detect and intercept.

Recent months have seen a sharp deterioration in ties between the two Koreas, with both sides jettisoning key tension-reducing agreements, ramping up frontier security, and conducting live-fire drills along the border.