The North sent dozens of artillery shells near Yeonpyeong Island just 50 miles from the South Korean mainland, the Yonhap news agency reports.
South Korean Defense Minister Kim Tae-young says the South is considering the installation of an artillery-tracking radar system on its islands near the Yellow Sea border.
Observers theorize the shelling may be part of North Korea's attempt to pressure the United States and the South Koreans to respond to its proposal for a peace treaty.
The two Koreas are still technically at war since the Korean War ended in a truce.
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