North, South Korea Exchange Fire

South Korea military officers fired at North Korea Wednesday, after marines on the island of Yeonpyeong spotted three artillery shells in nearby water. The shots were fired near the Northern Limit Line, which South Korea patrols and was drawn by the United Nations. North Korea, however, has long said that the line should be further south. The exchange increases tension between the two nations, after a North Korea attack killed four on the island in November.