North Korean leader Kim Jong Un has inspected a facility that produces nuclear material and called for bolstering the country’s nuclear capability, state media reports.

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 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 said Sunday that 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.

Seoul: North Korea announced Sunday that it had tested a cruise missile system, marking its third weapons display this year. The move comes as North Korea vows "the toughest" response to U.S.-South Korean military drills, which it deems a threat.

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

The action suggested North Korea will likely maintain its its confrontational stance against the U.S. for now, even though President Donald Trump said he intends to reach out to North Korean leader Kim Jong Un.

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.