Seoul:  In its latest response to military drills by South Korea and the United States, North Korea claimed on Saturday that it had tested yet another underwater nuclear attack drone. However, analysts have questioned whether Pyongyang actually has such a weapon.

North Korea recently conducted tests of an underwater nuclear-capable drone and an intercontinental ballistic missile launch, according to state media.

From April 4 to 7, a test of an underwater strategic weapon system was conducted in the DPRK, according to the official Korean Central News Agency. The "Haeil-2" underwater nuclear attack drone "cruised" for 71 hours and 6 minutes over a simulated distance of 1,000 km.

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The test warhead accurately detonated underwater, according to KCNA. The test successfully demonstrated the underwater strategic weapon system's dependability and its capacity for lethal attack. In less than three weeks, North Korea claims to have already conducted three underwater drone tests.

It claimed to have conducted the first test of the Haeil, which means "tsunami" in Korean, on March 23 and blamed US-South Korea exercises for a deteriorating regional security situation. Haeil is capable of unleashing a "radioactive tsunami." It announced that a second test had been conducted five days later.

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In response, Seoul was "capable of monitoring and detecting such drones infiltrating underwater," South Korean Defense Minister Lee Jong-sup informed MPs.

A high level of activity has also been seen in satellite images of North Korea's main nuclear facility following Kim Jong Un's directive to increase the production of nuclear material fit for use in weapons.

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

According to Seoul's military, South Korea and the US conducted joint air exercises on Wednesday that included at least one US B-52H strategic bomber with nuclear weapons capability.

North Korea has responded to other recent drills with a series of increasingly provocative banned weapons tests because it sees such exercises as invasion drills. Along with expanding its nuclear arsenal, North Korea is attempting to diversify its delivery systems.

Poseidon torpedoes with nuclear capability are reportedly a similar weapon that Russia has also developed, but experts said North Korea may not yet be able to master the complicated technology needed for such weaponry.

Though they should not be "easily dismissed for being exaggerated," Choi Gi-il, professor of military studies at Sangji University, cautioned AFP that the North's claims regarding the tests.

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"While the North may have overstated the degree of success to some extent, they seem to demonstrate Pyongyang's underlying confidence in this technology, some of which may have been imported from Russia," says the author. The transfer of the underwater drone technology has not received any official comments from Russia or North Korea, Choi continued.