North Korea has sent a letter to the United States protesting a planned combined military exercise with South Korea that will begin later this month.

The state-run Korean Central News Agency said the letter was sent Monday to the commander of U.S. forces in South Korea, Army Gen. James Thurman, in the name of Pak Rim-su of the Korean People’s Army.

The North claimed in the dispatch that South Korea and the U.S. are aiming to veil the aggressive nature of the Ulchi Freedom Guardian military drill, dismissing South Korea and the U.S.’s stance that the exercises are annual drills of a defense nature.

North Korea’s ruling Workers’ Party offical newspaper the Rodong Sinmun said Monday that there is no doubt the combined drill centers on training for the invasion of North Korea. The paper also claimed that there is no change in Pyongyang’s position that force should be countered with force.

The annual joint military exercises will begin on August 20th for an eleven-day run.