In an interview last week, President Trump called Kim Jong Un a "smart guy" and said he would reach out to the North Korean leader.

North Korea conducted another missile test while issuing a stern message to the United States. The test of a underwater-to-surface cruise missile comes just weeks after the country claimed to test a new hyper-sonic missile.

South Korea 's Yonhap News Agency said North Korea might be using a vertical cold-launch system to fire the missiles. The system, which is commonly associated with submarine- and ship-based weapons, ejects a missile from its container before the missile ignites midair.