North Korea on Monday said it used a ballistic missile launch to simulate a nuclear attack on neighbor South Korea over the weekend. 

North Korean leader Kim Jong Un oversaw the drill, according to Korean state media, as the country perceives “aggression” from enemies. It’s the latest demonstration in protest of joint military exercises from the U.S. and South Korea in the Korean Peninsula.

North Korea’s drill was “carried out under the tense situation in which a large-scale war drill is being frantically scaled up by the U.S.-South Korean allied forces to invade the DPRK and U.S. nuclear strategic assets are massively brought to South Korea,” according to state outlet Rodong Sinmun. 

The U.S. has moved to work with South Korea amid tensions in the Asian region, as China builds its relationship with Russia during its war on Ukraine and underscores its upset over Taiwan. 

North Korea said the ballistic missile launched as the nuclear simulator, tipped with a mock nuclear warhead, flew about 500 miles off the country’s eastern coast and exploded about 800 meters above targeted waters. The country claimed the drill had “no adverse effect on the security of the neighboring countries.”

Pyongyang has stepped up its show of nuclear force as the U.S. and South Korea conduct the military drills North Korea has interpreted as prep for a future invasion.

The Associated Press contributed to this report.