"(The missiles) appear to be targeting our fighter jets that fly near the Northern Limit Line (NLL)," the source said on customary condition of anonymity, referring to the Yellow Sea border.
South Korea and the U.S. on Sunday launched large-scale naval drills off the Korean Peninsula's west coast, far south of the border where four people were killed and 18 others wounded in Tuesday's surprise attack on Yeonpyeong Island.
The Soviet-designed SA-2 missile has a range of between 13 and 30 kilometers. Other missiles on the North's west coast, such as the Samlet and Silkworm with ranges of up to 95km, have also been put onto launch pads, the source said.
"The military is preparing for the possibility of further provocations as the North Korean military has deployed firepower near the NLL and is preparing to fire," the source said.