North Korea claimed on Friday that it had tested an underwater nuclear attack drone able to unleash a "radioactive tsunami."
They also blamed recent US-South Korea power exercises for a deteriorating regional security situation, reports AFP.
Pyongyang carried out drills in response this week, the official Korean Central News Agency said, including testing of the new underwater nuclear delivery system.
"This nuclear underwater attack drone can be deployed at any coast and port or towed by a surface ship for operation," the report said.
The weapon's mission is to "stealthily infiltrate into operational waters and make a super-scale radioactive tsunami ... to destroy naval striker groups and major operational ports of the enemy," it added.
North Korean leader Kim Jong Un personally oversaw the tests, KCNA reported, and images released by Pyongyang's Rodong Sinmun newspaper showed a smiling Kim and what appeared to be an underwater explosion.
The agency also said Pyongyang had fired strategic cruise missiles "tipped with a test warhead simulating a nuclear warhead" on Wednesday.
But analysts questioned North Korea's claims.
The idea that Pyongyang has "a nuclear-capable underwater drone should be met with skepticism," said Leif-Eric Easley, a professor at Ewha University in Seoul.
"Pyongyang's claims about a new weapons system are not the same as a credible demonstration of capability," he added.
In a Twitter post, US-based analyst Ankit Panda said it could not be ruled out that the announcement was "an attempt at deception/psyop".
Even so, the claim was "shocking," Cheong Seong-chang of the private Sejong Institute told AFP.
If true, it is hard to see how Seoul "could respond to such a formidable new weapon from North Korea that (it says) can completely destroy the South's major operational ports."
The KCNA statement also indicates "Pyongyang is more than ready to use its tactical nuclear weapons at any time," An Chan-il, a defector-turned-researcher, told AFP.
"This obviously further strengthens Kim's justification for his future nuclear tests."
Bd-pratidin English/Lutful Hoque
