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.

SEOUL, South Korea — North Korea unveiled for the first time a nuclear-powered submarine under construction, a weapons system that can pose a major security threat to South Korea and the U.S.

Last week's accidental shelling of a South Korean village occurred less than 20 miles from the border of the nuclear-armed North.

North Korea denounced joint military drills between the US and South Korea saying the South Korean Air Force’s recent bombing mistake shows the risk of the region unintentionally getting dragged into a new armed conflict.