North Korean leader Kim Jong Un presided over the unveiling ceremony on Wednesday, saying the new sub was part of a "push forward with the nuclear weaponization of the Navy in the future", according to KCNA.

The launching of the submarine, named the Hero Kim Kun Ok, "heralded the beginning of a new chapter for bolstering up the naval force of the DPRK", the KCNA report said, referring to the country by the abbreviation of its formal name.

During the festive ceremony that involved confetti and balloons, Kim stressed "the strategic and tactical plan to continuously enhance the modernity of underwater and surface forces and push forward with the nuclear weaponization of the Navy in the future", KCNA said.

On Thursday, Kim inspected the submarine as it was preparing for a test cruise.

"Saying that to arm the navy with nuclear weapons arises as an urgent task... he stressed the need to enable the Navy to successfully carry out its strategic duty by hastening the transfer of underwater and surface vessels equipped with tactical nuclear weapons to the Navy", Kim was reported as saying by KCNA.