South Korea and the U.S. have conducted an exercise on destroying North Korean chemical weapons, according to American military forces in Korea Sunday.

The U.S. Forces Korea (USFK) said troops participated in an exercise to remove the lethal nerve agent sarin at a shooting range in Paju, Gyeonggi Province, on Tuesday and Wednesday. The drill was part of the annual joint Key Resolve and Foal Eagle exercises.

During the exercise, the forces raided a mock North Korean chemical weapons factory and destroyed its products.

The American troops arrived in CH-47 Chinook and UH-60 Black Hawk helicopters.

From Feb. 13 to 17, the two allies conducted a drill at a live-fire complex in Pocheon, Gyeonggi Province, to seize and destroy North Korean weapons of mass destruction.

North Korea has 25 nerve agents, including VX that was used in the recent murder of Kim Jong-nam, the half-brother of the military state’s leader Kim Jong-un, according to the Korea Institute for Defense Analyses.