South Korea and the U.S. could face military action with “tremendous muscle” unless they cancel their Ulchi-Freedom Guardian exercises this month, North Korea warned Saturday. The annual training event is scheduled to begin Monday and end Aug. 28. When Seoul notified Pyongyang of its intention to participate, it sparked a big round of saber-rattling, USA Today reported.

“The further Ulchi-Freedom Guardian joint military exercises are intensified, the strongest military counteraction the [Democratic People’s Republic of Korea] will take to cope with them,” a representative of the North Korean National Defense Commission said in a statement. “The DPRK is the invincible power equipped with both the latest offensive and defensive means unknown to the world, including nuclear deterrence.”

Pyongyang has historically viewed Ulchi-Freedom Guardian drills as preparations for war. But Seoul has insisted the exercises, first conducted in 1976, are designed simply to enhance “readiness, protect the region and maintain stability on the Korean Peninsula,” as noted in a statement by U.S. Forces Korea. Plans this year call for the participation of troops representing Australia, Canada, Colombia, Denmark, France, New Zealand and the U.K., as well as South Korea and the U.S. 

Tension in the region was already high heading into the yearly training session. This month, two South Korean soldiers were injured by land-mine blasts inside the Demilitarized Zone, a buffer between the countries. North Korea has denied any involvement in the incident.

This week, North Korea threatened to turn South Korea into a “sea of fire” if it continued sending propaganda pamphlets across the border.

However, a military expert told CNN that North Korean leader Kim Jong Un may be bluffing about launching a war as a show of force.

“One of the key propaganda goals of the young leader is to just get on the radar of the U.S.,” retired Army Lt. Gen. Mark Hertling said. “With all the other things we’re focused on — ISIS, al Qaida in the Arabian Peninsula, Russia and Ukraine, etc. — Kim Jong Un wants to ensure he grabs attention.”