State media released photos showing what it called “a nuclear-powered strategic guided missile submarine,” as it reported leader Kim Jong Un’s visits to major shipyards.

Yonhap, a South Korean news agency, said this was the first time Pyongyang had publicly disclosed the construction of such a vessel. In 2021, Kim pledged to introduce a nuclear-power submarine in response to what he called escalating military threats from the U.S., and Washington will no doubt be concerned about the development.