South Korea and the United States began an annual, joint military exercise Monday, despite threats from North Korea last week that it would launch a “sacred war” if its territory is encroached upon.

A spokesman at South Korea's Defense Ministry called the exercise routine, explaining it will be similar in scope and size to last year's drill.

The North's official state media say supreme commander Kim Jong Un has personally ordered a frontier unit to be prepared for battle.

There is no indication of unusual military movements in the North.

In a statement Saturday, the North's National Defense Commission said the maneuvers are a “silent declaration of war” that will prompt a “corresponding physical retaliation” by Pyongyang. The statement called the war games “an outright challenge to the peace and security of the Korean peninsula and an explicit act of destruction.”

South Korea and the U.S. regularly hold military exercises to bolster their readiness against possible North Korean aggression. Still, the North routinely denounces military drills in the South as rehearsals for invasion.