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 said Sunday it tested a cruise missile system, its third known weapons display this year, and vowed “the toughest” response to what it called the escalation of U.S.-South Korean military drills that target the North.

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

North Korea announced 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.

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North Korea has test-fired sea-to-surface strategic cruise guided missiles, the North's state media reported Sunday, quoting Kim as saying that Pyongyang's deterrence means are being perfected.

North Korea test-fired strategic cruise missiles on Saturday the official Korean Central News Agency reported, marking a third launch this month as Donald Trump returned to power in the US.

North Korea has tested sea-to-surface strategic cruise guided missiles, Pyongyang's state media reported on Sunday. State-controlled KCNA news agency quoted the country's Missile Administration as stating the test-fire,