"Our navy fired warning shots to stop the incursion by a North Korean fishing boat, which has intruded into our waters, ignoring our loud-speaker warning," a Joint Chiefs of Staff spokesman said.

The midday incursion lasted five minutes before the boat returned to North Korean waters, he added.

It was the latest in a series of incursions from the North reported by South Korean military authorities over the past nine days.

Warning shots were fired two days ago to deter a North Korean incursion into the sea off the west of the Korean peninsula.

The spokeman said the warning shots were fired from close range, about 270 metres (900 feet) away, from a naval vessel cruising close to the Northern Limit Line (NLL), the de-facto inter-Korean maritime border.

WAR.WIRE