North Korea said Tuesday that it has entered its "number one combat readiness posture."

The North Korean military's Supreme Command said in a statement that it will boast the determination of its army and people to protect its sovereignty and dignity through actual military action.

The statement continued that North Korea can no longer tolerate the situation where its sovereignty is violated and the U.S. nuclear threat is turning into a reality.

The statement said that the "number one combat readiness posture" applies to all field artillery units including the strategic rocket and long-range missile units that target the enemies in the U.S., South Korea and the surrounding region.

A South Korean military official said that this is the first time that the North used the term, ""number one combat readiness posture." The official said that given the use of the word, "number one," it appears Kim Jong-un has issued the order to his missile and rocket units to maintain the highest level of readiness.

Earlier Tuesday, South Korea’s military said it believes North Korea began a nationwide military exercise on Monday with participation from its Army, Navy and Air Force. The South’s military said its working to determine the exact scope of the drill.