North and South Korea have both for the first time fired missiles across their maritime border.
On Wednesday, the South retaliated three hours after Pyongyang fired a missile which landed less than 60km from its eastern city of Sokcho.
South fired three air-to-ground missiles in response, which officials said landed a similar distance past the Northern Limit Line.
The South said the North fired at least 10 missiles on Wednesday. These are believed to be in response to joint military drills being carried out by the US and South Korea this week.
The launch had triggered air-raid sirens on Ulleung, and residents were told to evacuate to underground shelters.South Korea’s President Yoon Suk-yeol labelled it an “effective territorial invasion” and vowed a “swift and firm response”.
However, countries technically only have a right to establish its territorial sea to a limit not exceeding 12 nautical miles (22km).