South Korea’s military says its navy has fired three warning shots towards North Korea in retaliation for artillery shells from the North which landed near Yeonpyeong island.
The North Korean artillery was the result of an apparent training exercise near the tense maritime border.
Three shells reportedly landed near the disputed Northern Limit Line.
Last November Yeonpyeong island was attacked by the North, and four people were killed. South Korea responded by sending more troops and vowing to retaliate more forcefully in future.
Pyongyang said it had been responding to military exercises carried out by the South.
The sinking of a South Korean warship causing the deaths of 46 sailors was also blamed on the North.
But this year tensions have eased since North Korea renewed calls for dialogue. Talks aimed at ending Pyongyang’s nuclear programme have been resumed.