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.

North Korea announced that it had performed a test of its cruise missile system on Saturday. It was the communist country’s fourth known missile launch since November and the second in less than a week since President Donald Trump ’s inauguration.

North Korea's foreign ministry vowed the "toughest counteraction" against the United States as long as Washington "refuses" the country's sovereignty.