Seoul, South Korea (CNN) -- South Korea fired back at North Korea on Wednesday after it said three shots from the North hit waters close to the maritime border.
There were no casualties reported, the South Korean defense ministry said.
Tensions between the neighbors heightened last year after 50 South Koreans were killed in two separate incidents.
In November, the South accused North Korea of shelling Yeonpyeong Island, near the border between the two sides. The incident killed two South Korean marines and two civilians.
North Korea said the shelling was in retaliation for the South's navy firing into Northern waters.
And in March 2010, South Korea accused the North of torpedoing and sinking one of its warships, killing 46 sailors.
North Korea denies attacking the warship Cheonan, though a Seoul-led international investigation found that a North Korean mini-submarine responsible.
Tensions remained high after talks between North and South Korea collapsed in February when the two sides failed to reach an agreement on securing high-level military discussions.