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.

Kim Jong Un is aiming to increase North Korea's nuclear weapons capability as the U.S. remains cautious about the country's alliance with Russia in the Ukraine war.

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.