North Korea on Thursday showcased what appeared to be significant progress on a nuclear-powered submarine, with state media releasing new images as leader Kim Jong Un criticized South Korea’s parallel push to develop the same capability.

The North’s Korean Central News Agency said Kim toured a shipyard housing an 8,700-ton-class nuclear-propelled submarine, a project Pyongyang has framed as central to modernizing and nuclear-arming its navy. The vessel, which the regime has described as a “strategic guided missile submarine,” is intended to carry nuclear weapons, according to previous statements.