North and South Korea have fired missiles into each other’s coastal waters for the first time.
Seoul retaliated on Wednesday three hours after Pyongyang fired a missile that landed less than 60 kilometers (37 mi) from the southern city of Sokcho.
The South’s army said that this was an “unacceptable” violation of its territory.
The military reportedly fired three air-to-surface missiles in response, which officials said landed at a similar distance across the Northern Frontier Line (NLL).
The demarcation line marks the approximate midway point in the sea between North and South Korea, but the North has never acknowledged the border.
On Tuesday, North Korea warned that South Korea and the US would pay “the most terrible price in history” if joint military exercises, seen as a veiled threat to use nuclear weapons, continue.
The North is expected to resume nuclear weapons testing soon after a five-year hiatus, with US and South Korean intelligence saying Pyongyang has completed all necessary preparations.