North Korea confirmed Friday that it this week tested a submarine capable of launching a nuclear attack that can "cause a large-scale radiological tsunami" through an underwater explosion, while blaming the deterioration of regional security on joint military exercises of the United States and South Korea.

And North Korea's official news agency reported Friday that the North Korean army deployed and tested, during exercises that lasted from Tuesday to Thursday off South Hamgyong Province, a new weapon system whose mission is to "cause a large-scale radioactive tsunami" through an underwater explosion to destroy enemy ships and ports.

She indicated that this submarine "can be deployed on any coast or port and towed by a surface ship."

And the agency stated that the "secret weapon" was placed on Tuesday in the waters off South Hamgyong Province, and on Thursday it detonated an experimental warhead.

North Korean leader Kim Jong Un "directed" the exercise and said it should serve as a warning to the United States and South Korea to "realize the DPRK's unlimited deterrence capacity...", using North Korea's official name.

KCNA said Kim "expressed his desire to make the US imperialists and the puppet regime in South Korea sink into despair."

North Korea fired several cruise missiles on Wednesday, according to the South Korean military, which is currently conducting large-scale joint exercises with the United States.

However, analysts questioned North Korea's assertions.

Professor Lev-Eric Easley of Ewha University in Seoul said that the idea of Pyongyang possessing "a drone capable of carrying nuclear weapons should be met with skepticism."

"Pyongyang's assertions about a new weapons system are different from reliable proof of its capabilities," he added.

In a tweet, the American analyst, Ankit Panda, did not rule out that the test was "an attempted deception / psychological operation."

But despite everything, these assurances are "shocking", Xiong Seong-chang of Sejong Institute told AFP.

And if that is true, it would be difficult to know how Seoul would respond "to such a new North Korean weapon that (as it says) could completely destroy the main operating ports in the South."

The North's official KCNA news agency also said that "Pyongyang is more than ready to use its tactical nuclear weapons at any time," researcher An Chan-il told AFP.

Russia may also have developed a similar weapon -- the nuclear-capable Poseidon torpedoes -- but mastering the complex technology required for such weapons is still out of North Korea's reach, analysts say.

"For a submarine that cannot be detected, it requires advanced technology such as control sensors and radar," Sanji University military studies professor Choi Gi-il told AFP.

After a year that saw a record number of weapons tests and growing nuclear threats from Pyongyang, Seoul and Washington stepped up defense cooperation and held the largest joint military exercises in five years from March 13 to 23, 2023.

North Korea regards the maneuvers as rehearsals for an invasion of its territory and has repeatedly warned that it will take "crushing" measures in response.

And described the North Korean news agency on Friday joint exercises between the United States and South Korea, which was called "Freedom Shield" (Shield of freedom) as a maneuver aimed at "occupying" North Korea.

The agency said that the "underwater nuclear attack" exercises conducted by Pyongyang were "with the aim of warning the enemy of a real nuclear crisis."

Kim Jong Un also noted that North Korea's nuclear capabilities are "enhancing at a faster rate," according to KCNA.

In the year 2022, North Korea has said its nuclear power status is "irreversible" and has conducted a record number of ballistic tests, in violation of UN resolutions. The North Korean leader recently called for a massive increase in the country's weapons production, including tactical nuclear weapons.

For its part, Washington has repeatedly affirmed its "unwavering" commitment to the defense of South Korea, by using "the full range of its military capabilities, including nuclear," and recently sought to reassure Seoul of its expanded deterrent capabilities with its allies.

This comes as South Korea seeks to reassure a somewhat anxious public about US commitments regarding the so-called extended deterrence that can prevent attacks against allies, thanks to US military means, including nuclear weapons.

Friday's statement comes a week after Pyongyang tested its most powerful missile, the Hwasong-17, in its second intercontinental ballistic missile test this year.