North Korea fired several cruise missiles into the waters off its west coast on Tuesday, Seoul`s military said, the latest in a string of weapons tests carried out by Pyongyang this year.
South Korea`s military "detected several unknown cruise missiles launched into the West Sea of North Korea around 07:00 (2200 GMT)", Seoul`s Joint Chiefs of Staff said in a statement.
South Korean and US intelligence agencies "are conducting a detailed analysis," the JCS said.
"Our military is cooperating closely with the U.S. while strengthening surveillance and vigilance, and is closely monitoring North Korea`s activities," it added.
Unlike their ballistic counterparts, the testing of cruise missiles is not banned under current UN sanctions on Pyongyang.
Cruise missiles tend to be jet-propelled and fly at a lower altitude than more sophisticated ballistic missiles, making them harder to detect and intercept.
Recent months have seen a sharp deterioration in ties between the two Koreas, with both sides jettisoning key tension-reducing agreements, ramping up frontier security, and conducting live-fire drills along the border.
Pyongyang has accelerated weapons testing in the new year, including tests of what it called an "underwater nuclear weapon system" and a solid-fuelled hypersonic ballistic missile.
On Monday, state media said North Korean leader Kim Jong Un had overseen the test launch of a new strategic cruise missile from a submarine.
Photos showed a missile soaring into the sky from the water, leaving a huge trail of white smoke, but it was not clear if it had been fired from a submarine.
In recent weeks, Kim has declared the South his country`s "principal enemy", jettisoned agencies dedicated to reunification and outreach and threatened war over "even 0.001 mm" of territorial infringement.
He also said Pyongyang would not recognise the two countries` de facto maritime border, the Northern Limit Line, and called for constitutional changes allowing the North to "occupy" Seoul in war, the Korean Central News Agency said.
`Overwhelming response`
In Seoul, President Yoon Suk Yeol told his cabinet that should the nuclear-armed North carry out a provocation, South Korea would hit back with a response "multiple times stronger", pointing to his military`s "overwhelming response capabilities".
Pyongyang`s latest launch comes after South Korea conducted a 10-day special forces infiltration drill off the country`s east coast, "in light of serious security situations" with the North, which ended January 25.
At North Korea`s year-end policy meetings, Kim threatened a nuclear attack on the South and called for a build-up of his country`s military arsenal ahead of armed conflict he warned could "break out any time".
Earlier this month, the North launched a solid-fuel hypersonic missile, just days after Pyongyang staged live-fire exercises near the country`s tense maritime border with South Korea, which prompted counter-exercises and evacuation orders for some border islands belonging to the South.
Kim also successfully put a spy satellite into orbit late last year, after receiving what Seoul said was Russian help, in exchange for arms transfers for Moscow`s war in Ukraine.
