The U.S. Department of Defense has said that the ongoing South Korea-U.S. joint military exercise is defensive in nature, dismissing North Korea’s claim that the exercise is an “invasion rehearsal.”

Pentagon spokesperson Patrick Ryder made the remarks during a press briefing on Tuesday when asked to comment on the North’s accusation.

Calling the North’s claim “patently false,” Ryder said that these exercises are longstanding and defensive in nature, and that they provide an opportunity for the two nations' forces to work together on interoperability and learn to operate in varied environments.

The remarks came after the North Korean foreign ministry’s Institute for American Studies on Sunday denounced the joint military exercise as “war drills for aggression,” warning that the North would maintain the balance of power for preventing war by stockpiling the greatest deterrence. 

South Korea and the United States kicked off the Ulchi Freedom Shield exercise on Monday, which will run through August 29. The exercise will include a computer simulation-based command post exercise and field training.