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

North Korea conducted a test of strategic cruise missiles from the sea, overseen by Kim Jong Un, KCNA reports. North Korea conducted a test of strategic cruise missiles from the sea on Saturday. This information was reported by the North Korean agency KCNA on Sunday morning local time.