The North's state-run news agency said the missile, a "Hwasal-2", was fired into the West Sea on Tuesday.

The launch was first noted by Seoul's military, which said it had detected several cruise missiles.

KCNA said the drill was meant to check the army's "rapid counterattack posture" as well as improve "its strategic striking capability".

It added that the launch had "no adverse effect on the security" of neighbouring countries.

This month, Pyongyang has conducted tests of what it called an "underwater nuclear weapon system", a solid-fuelled hypersonic ballistic missile, and a new generation of strategic cruise missiles.

The Hwasal-2 strategic cruise missile has been test-fired before by the North.

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

Despite rafts of UN sanctions, Seoul and Washington say the North's leader, Kim Jong Un, has been shipping weapons to Russia, possibly in exchange for Moscow's technical assistance in Pyongyang's budding spy satellite programme.

The test launch also comes as relations between the two Koreas have sharply deteriorated, with Kim declaring Seoul his principal enemy.