North Korea said Saturday it carried out another test of an underwater nuclear-capable attack drone this week, proving the weapon system's reliability and "fatal" striking capability.

The North tested the Haeil-2 underwater strategic weapon system from April 4-7, according to the Korean Central News Agency (KCNA).

"The system will serve as an advantageous and prospective military potential of the armed forces of the DPRK essential for containing all evolving military actions of enemies, removing threats and defending the country," the KCNA said in an English-language dispatch.

DPRK stands for the North's official name, the Democratic People's Republic of Korea.

The North's provocation came as the secretive regime has vowed to take "overwhelming" actions against joint military drills between South Korea and the United States.

The test drone was deployed from a port in South Hamgyong Province on Tuesday, and "correctly set off" a test warhead underwater Friday after cruising along an "oval and eight-shaped" course simulating a distance of 1,000 kilometers for 71 hours and six minutes, it added.

The provocation came about two weeks after the North first made public a test of its underwater attack drone Haeil on March 24. It claimed the "secret weapon" is capable of generating a "radioactive tsunami" and stealthily attacking enemies.

On March 28, the regime unveiled its Hwasan-31 tactical nuclear warhead for the first time and claimed that it had staged an underwater detonation test of its Haeil-1 drone a day earlier.

Considering the change in the weapon's name in the latest test, the North could have tested an improved version of the Haeil this week, observers said.

The North has recently intensified its provocative acts, such as the unveiling of the Hwasan-31 tactical nuclear warhead and the launch of cruise missiles from a submarine.

Observers said the North is likely to bolster its weapons tests on key anniversaries this month, namely the 111th birthday of late North Korean founder Kim Il-sung on April 15. (Yonhap)