South Korea's military fired artillery towards North Korea on Wednesday in response after artillery shells from the North landed near the disputed sea border, Yonhap news agency has reported.
A South Korean Defense Ministry official said the rounds fired by the North had landed off its Yeonpyeong Island. It is not clear on which side of the border it was.
There were no immediate reports of damage or injuries.
South Korea's YTN TV said the incident was provoked by military exercises being held by the North near the volatile Yellow Sea border.
The North shelled Yeonpyeong last November, killing four people, just months after the alleged North Korean sinking of a South Korean warship.
The two Koreas, who technically remain at war following the 1950-53 Korean War, agreed last month to return to six-party talks aimed at ending North Korea's nuclear program.
