From Chosunilbo:

North Korea has deployed multiple rocket launchers along the shore north of Yeonpyeong, Baeknyeong and Gangwha islands in response to a planned South Korean artillery drill on Yeonpyeong, government sources here say. The North earlier threatened an "unpredicted self-defense counterattack" to the drills.

A South Korean government source said, "After making the threat in a message sent Friday, North Korea raised the alert level at artillery divisions on the west coast and deployed the multiple rocket launchers." The source added the South Korean military is monitoring the situation.