State media in North Korea claims its military has tested a nuclear underwater drone that could release a 'radioactive tsunami'
North Korea is continuing to ramp up its weapons testing.
State media reports that its military has tested an underwater nuclear attack drone designed to unleash what it called a "radioactive tsunami" that would destroy enemy naval vessels and ports.
The KCNA news agency said during the drills from Tuesday through Thursday the North Korean military deployed and test-fired the new weapon system which is designed to set off such a "super-scale" destructive wave,
"This nuclear underwater attack drone can be deployed at any coast and port or towed by a surface ship for operation," KCNA said.
The agency said the weapon was put in the water off South Hamgyon province on Tuesday, and on Thursday it detonated a test warhead.
Up to that point, it had cruised for 59 hours and 12 minutes at a depth of 80 to 150 meters, the agency reported.
North Korean leader Kim Jong Un, who reportedly "guided" the drill, said it should serve as a warning for the United States and South Korea to "realise the DPRK's unlimited nuclear war deterrence capability being bolstered up at a greater speed".
DPRK is the acronym for North Korea's official name.
More tests, more often
After a record-breaking year of weapons tests and growing nuclear threats from Pyongyang, Seoul and Washington have ramped up security cooperation, and on March 13 kicked off their largest joint military drills in five years, known as Freedom Shield.
KCNA said that on Wednesday the North also fired strategic cruise missiles "tipped with a test warhead simulating a nuclear warhead".
The South Korean military had reported the firing of multiple cruise missiles from the North on Wednesday.
That launch comes about a week after Pyongyang test-fired its largest and most powerful missile, a Hwasong-17, its second intercontinental ballistic missile (ICBM) test this year.
The North's state media described the ICBM launch as a response to the ongoing, "frantic" US-South Korea drills.
North Korea last year declared itself an "irreversible" nuclear power and Kim recently called for an "exponential" increase in weapons production, including tactical nuclear weapons.