North Korea announced Saturday that it had conducted a new test of a "unmanned" nuclear submarine , in the latest response to the US-South Korean maneuvers, using technology that still raises questions about Pyongyang's possession of it.

"The DPRK's National Defense Science Research Institute conducted a test of a strategic underwater weapon system between April 4 and 7," North Korea's official KCNA news agency reported. It added that the Hale-2 nuclear-powered submarine conducted "simulations under water, during which it covered a distance of 1,000 km."

North Korea announced on March 23 the first test of this submarine, which, it said, is capable of "causing a large-scale radioactive tsunami" through an underwater explosion.

The agency indicated that the weapon "detonated accurately underwater," pointing out that this test "proves the reliability of the strategic underwater weapon system and its lethal offensive ability."

This is the third test of this system announced by North Korea, after two previous tests, the first on March 23 and the second announced on the 28th of the month.

Russia also announced the development of a similar weapon, the nuclear-capable Poseidon torpedo, but experts believe that North Korea does not yet possess the high-tech technology required for this type of weapon.

But Choi Ji-il, a professor of military studies at Sangji University, told AFP that "even if the North somewhat exaggerated the level of success (the tests), it seems to show Pyongyang's confidence in this technology."

He warned that the North's assertions should not be "disregarded" under the pretext that it is exaggerated, stressing that it cannot be ruled out that Russia has transferred technology for this type of weapon to Pyongyang.

On April 5, Seoul and Washington conducted joint air exercises that included at least one US nuclear-capable B-52H bomber, according to the South Korean military.

After a year that saw a record number of weapons tests and growing nuclear threats from Pyongyang, Seoul and Washington strengthened their 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.

The North confirmed in particular that on March 16 it tested an intercontinental ballistic missile.

North Korea last year declared itself an "irreversible" nuclear power, and Kim recently called for a "massive" increase in weapons production, including tactical nuclear ones.

Satellite images taken a month ago revealed a high level of activity at the main North Korean nuclear complex in Yongbyon, according to the US-based "38 North" organization.