Military authorities are analyzing data after detecting signs of North Korea building a large-scale submarine in an area that houses submarine-related facilities. 

The military said Tuesday that it identified images of the North building a submarine in Sinpo, South Hamgyong Province. 

The military has reportedly assessed that the watercraft could be a nuclear-powered submarine that North Korean leader Kim Jong-un had mentioned in September of last year. 

Seoul's military believes that though Pyongyang is unlikely to have key equipment to build a nuclear-powered submarine, the reclusive state could have produced such watercraft given that the said submarine is reportedly larger than the North’s existing submarines.

On September 8 of last year, the North Korean leader disclosed plans to build a nuclear-powered submarine when he unveiled the “Hero Kim Kun Ok,” describing it as a “tactical nuclear attack submarine.”