North Korea has released its first pictures of a nuclear-powered submarine under construction, which could dramatically change the security calculus in the region.

State media released a bulletin on Saturday with photos of dictator Kim Jong-un visiting a North Korean shipyard that is said to build military vessels.

On the visit, Kim “learned about the building of a nuclear-powered strategic guided missile submarine” as part of the country’s “important goals … for building the country into an advanced maritime power,” the bulletin said.

The release of the pictures comes before the US and South Korea are due to begin their annual Freedom Shield joint military exercises, which start on Monday and run until March 20.

North Korea has ramped up criticism ahead of these drills, as it does each year, with state media saying they “deteriorate circumstances in the Korean Peninsula”.