The United States and South Korea on Monday launched their largest joint military drills in years amid ongoing tensions with North Korea.

Kim Jong Un, leader of the isolated nation, has increased weapons testing and threatened to deploy nuclear weapons against the U.S. and neighboring South Korea. 

The Defense Department said last week the Ulchi Freedom Shield exercises are intended to "bolster combined readiness" for the U.S. and South Korea.

Leaders from both countries are "committed to expanding the scope and scale of combined military exercises and training," the agency also said.

North Korea is using the exercises to justify its development of nuclear weapons and missiles, the Associated Press reports.