North Korea announced, on Saturday, that it had conducted a new test of an unmanned nuclear submarine, in the latest show of force over the joint exercises conducted by the United States and South Korea.
"The DPRK's National Defense Science Research Institute conducted a test of a strategic underwater weapon system between April 4 and 7," the official North Korean news agency KCNA reported.
It added that the "Hill-2" piloted nuclear submarine conducted an underwater simulation, during which it covered a distance of 1,000 kilometers over a period of 71 hours and 6 minutes.
The agency indicated that the submarine fired a warhead that "detonated accurately underwater," pointing out that this test "proves the reliability of the underwater strategic weapons system and its lethal offensive ability."
This test came about two weeks after the unveiling of a new system for unmanned submarines called "HAIL-1", which means tsunami in Korean, and is designed to carry out surprise attacks in "enemy waters".
On March 23, North Korea announced the first test of this submarine, which it said was capable of launching a nuclear attack that could "cause a large-scale radioactive tsunami" through an underwater explosion.
Analysts say North Korea is showing off its various nuclear capabilities against Washington and Seoul, although both sides question whether those submarines are operational.
After a year that witnessed a record number of weapons tests and growing nuclear threats from Pyongyang, Seoul and Washington strengthened defense cooperation and held the largest joint military exercises in 5 years from March 13 to 23.
Seoul and Washington carried out joint air exercises on April 5 that included at least one US B-52H bomber capable of carrying nuclear weapons, according to the South Korean military.
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.