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

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 condemned an upcoming U.S.-South Korea joint military exercise Friday, saying that "counteraction is inevitable" and warning that the allies would "pay dearly."

Russian Foreign Ministry spokeswoman said Thursday that Moscow believes Pyongyang's measures to 'strengthen defense capabilities' are 'fully justified under conditions of current escalation' - Anadolu

But analysts suggest Washington may be open to resuming talks with North Korea, with Moscow potentially playing the role of mediator.

An attack on South Korean reactors or spent fuel storage pools would release large amounts of radioactivity and cause massive evacuations, diverting attention from a possible strategic crisis in East Asia.

South Korea's humanitarian assistance to longtime rival North Korea reached zero last year for the first time in nearly 30 years as Pyongyang refused to accept aid.

Kim Jong Un is aiming to increase North Korea's nuclear weapons capability as the U.S. remains cautious about the country's alliance with Russia in the Ukraine war.