Only a handful of countries have nuclear-powered submarines. Last fall, US President Donald Trump promised assistance with advanced military technology to its democratic neighbor South Korea to build one.
Pyongyang views Seoul's ambitions to develop nuclear-powered submarines as "an offensive act that seriously violates North Korea's security and maritime sovereignty," Kim Jong-Un said, according to KCNA.
The images of the submarine raise speculation about whether Russia helped North Korea build a nuclear-powered submarine, Hong Min, an analyst at the South Korean think tank Korea Institute for National Unification, told AFP.
North Korea and Russia have been growing closer since Moscow launched its full-scale invasion of Ukraine nearly four years ago, and Pyongyang has sent troops to fight on the Russian side.
South Korean and Western intelligence agencies estimate that North Korea has sent thousands of soldiers, mainly to Kursk, along with artillery shells, rockets and long-range missile systems.
Corrected: In an earlier version of the text, the fuel for the submarines was incorrectly stated.
