North Korea has unveiled for the first time what it says is a nuclear-powered submarine under construction, a weapons system that can pose a major security threat to South Korea and the US.

Everything we know about North Korea’s nuclear-powered submarine - Photos released by Pyongyang suggest new naval vessel could carry about 10 nuclear-capable missiles

North Korea has long vied for nuclear-powered submarines, which would allow it to fire missiles from underwater. Advanced detection of the weapons is difficult, making the country’s construction of the warships worrisome.