NNorth Korea says it has tested an “underwater nuclear weapon system”. The North Korean Defense Ministry said on Friday that it was a response to joint naval exercises between South Korea, Japan and the USA, according to the state news agency KCNA. These maneuvers, in which a nuclear-powered US aircraft carrier also took part, “seriously threatened” North Korea’s security.

That's why North Korea tested its underwater nuclear weapon system “Haeil-5-23” in the East Sea, KCNA reported, citing the Defense Ministry. Last year, Pyongyang said it tested a nuclear underwater drone that could trigger a “radioactive tsunami,” analysts said At the time, however, there were doubts that North Korea had such a weapon.

Relations between South Korea and North Korea, which is largely isolated internationally, are at a low point. North Korea's leader Kim wants to expand weapons development, including tactical nuclear weapons. In response, South Korea, Japan and the United States have increased defense cooperation and held joint military exercises.