KCNA said the test-fire on Wednesday aimed to examine the reliability of the country's war deterrents and improve the navy's ability to perform strategic missions. One of the missiles was a Pulhwasal-3-31, the same type of strategic cruise missile North Korea said it test-fired from land last week.
Senior military officers observed the tests, which were conducted at sea off the country's east coast. KCNA added that the tests had no adverse impact on the security of neighbouring countries.
North Korea is not yet believed to have launched a modern missile submarine in full operation. Building such a submarine is a top military priority for leader Kim Jong Un, who has overseen the development of a range of strategic ballistic and cruise missiles. Last year, Kim criticised a nuclear submarine deal between the United States and South Korea while touring his country's submarine production facility, where state media images showed an 8,700-tonne nuclear-powered missile submarine under construction. He described the deal as a threat to the stability of the Korean Peninsula, KCNA reported.
The latest launch is part of a flurry of missile activity in recent weeks. Earlier this week, North Korea fired multiple ballistic missiles towards the sea off its east coast. On October 3, it tested a hypersonic intermediate-range missile designed to evade missile defences in South Korea and Japan.
After the ballistic missile launch, Seoul's Joint Chiefs of Staff spokesperson Jang Do-young said the move appeared to be a show of force, coming days after South Korea tested its own hypersonic weapon. Last week, South Korean President Lee Jae Myung oversaw the country's first test firing of a hypersonic missile, a rare public showcase of a missile test by a South Korean president. Lee's office said the weapon, once fully developed, would enhance South Korea's ability to strike key targets by surprise in the "Korean Peninsula theatre of operations".
Inter-Korean relations have further soured amid a dispute over a landmine incident in the Demilitarized Zone, with South Korea considering steps to pressure North Korea over the matter.