North Korea carried out a similar drill on March 31 during which shells dropped into South's territorial waters. (Photo: EPA)

(VOVworld) – North Korea on Tuesday conducted live-fire drills near the maritime border (NLL) in the Yellow Sea, hours after Pyongyang sent an announcement to Seoul. The South Korean army was put on high military alert and had permission to respond in case North Korean shells fall in its waters. This is the second time in a month that North Korea has carried out such drills.