This March 24 photo released by North's official Korean Central News Agency shows the test warhead of an "underwater nuclear attack drone" detonating underwater after it was launched off the coast of Riwon County, South Hamgyong Province, March 21. Yonhap

North Korea tested a new underwater nuclear weapon earlier this week capable of spawning a "radioactive tsunami" and stealthily attacking enemies, Pyongyang's state media said Friday.

Separately, the North also conducted a cruise missile drill using missiles "tipped with a test warhead simulating a nuclear warhead" as it slammed the combined military exercises between South Korea and the United States as an "actual drill" for "occupying" Pyongyang, according to the official Korean Central News Agency (KCNA).

The Central Military Commission of the North's ruling Worker's Party (WPK) commanded the drills from March 21 to 23 "in order to alert the enemy to an actual nuclear crisis and verify the reliability of the nuclear force for self-defense," the KCNA reported.

The "underwater nuclear attack drone" was deployed off the coast of Riwon County, South Hamgyong Province, on Tuesday and reached the target point in the waters off Hongwon Bay set as a mock enemy port with its test warhead detonating underwater Thursday afternoon, it said.

The drone cruised is reported to have traveled along an oval and figure-8 course at an underwater depth of 80 to 150 meters in the East Sea of Korea for 59 hours and 12 minutes.

The North claimed that the drones, designed to "stealthily infiltrate into operational waters and make a super-scale radioactive tsunami" to destroy naval striker groups and major ports of its enemies, can be deployed "at any coast and port or towed by a surface ship for operation."

North Korea began developing such underwater nuclear weapons in 2012 to "outpace the military and technical superiority of the imperialist aggressor forces," the KCNA said.

The "secret weapon" was named "unmanned underwater nuclear attack craft 'Haeil'" at the eighth congress of the WPK in 2021 and has undergone more than 50 shakedowns in the past two years, it added.

This March 24 photo released by the North's official Korean Central News Agency shows a strategic cruise missile of North Korea being launched in South Hamgyong Province, March 22. Yonhap

On March 22, the North also test-fired strategic cruise missiles "tipped with a test warhead simulating a nuclear warhead," according to the KCNA.

It said two "Hwasal-1" strategic cruise missiles and two "Hwasal-2" strategic cruise missiles, launched in South Hamgyong Province, accurately hit the target set in the East Sea.

The missiles flew on their "programmed 1500km- and 1800km-long oval and figure-8 orbits for 7,557 to 7,567 seconds and 9,118 to 9,129 seconds respectively," it added.

As he guided the "important military activities," leader Kim Jong-un "expressed his will to make the U.S. imperialists and the South Korean puppet regime plunge into despair for their choice through the high-profile demonstration of the powerful war deterrence" and to make them understand that they are bound to "lose more than they get" as they expand combined exercises in the region.

He stressed the need to take "offensive actions" to make the enemy realize the North's "unlimited nuclear war deterrence capability" and "seriously warned" the allies to stop their "reckless" war drills.

This March 24 photo released by North's official Korean Central News Agency (KCNA) shows North Korean leader Kim Jong-un watching a strategic cruise missile being launched in South Hamgyong Province, March 22. Yonhap

The KCNA slammed the U.S. and the "South Korean puppet regime of traitors" for staging "intentional, persistent and provocative war drills," saying that the exercises have "driven the military and political situation of the Korean peninsula to an irreversibly dangerous point."

South Korea's military earlier said it detected multiple cruise missile launches from the North's eastern city of Hamhung on Wednesday morning. (Yonhap)