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 says 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.

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

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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.