The announcement came amid fears that Pyongyang may be receiving crucial military technology from Russia in return for sending troops and weapons for its war against Ukraine.

North Korea currently has an estimated 70 to 90 submarines, but most are old and can only launch torpedoes and mines, not missiles.

North Korea has unveiled for the first time what it says is a nuclear-powered submarine under construction, a weapons system that can pose a major security threat to South Korea and the US.