— South Korean naval forces returned fire Wednesday after North Korea fired three artillery shells toward the disputed sea border between the two countries, the South’s Defense Ministry said.

At least one of the North’s shells, according to preliminary findings, landed in the area of the border, known as the Northern Limit Line, said a spokesman for South Korea’s Joint Chiefs of Staff, adding that the South broadcast a warning before firing three shells of its own.

North Korea called the claim “preposterous,” saying Thursday that the South overreacted to “normal blasting” from a construction project.

The incident, though minor compared with other recent military exchanges, underscored the volatility of relations between the North and South, particularly in the waters on the western side of the Korean Peninsula. The Northern Limit Line was drawn in 1953 — the South recognizes it, but the North does not — and it is not considered an official international maritime boundary.

Wednesday’s exchange of fire occurred in the vicinity of Yeonpyeong Island, a South Korean military and civilian outpost in territory the North claims. Relations between the neighbors sank to a low last year with a pair of deadly provocations in the disputed area — the March 26 torpedoing of a South Korean warship and the Nov. 23 shelling of Yeonpyeong. The incidents resulted in the deaths of 48 South Korean service members and two civilians.

Since the 1953 armistice ending the Korean War, the North and South have often clashed in the Yellow Sea, with boat seizures, exchanges of cannon fire and other hostile actions. A December 2010 report compiled by the International Crisis Group said that “this boundary in the Yellow Sea has the greatest potential to trigger a second Korean war.”

In recent weeks, North and South Korea have tried to improve relations, notably with a meeting of nuclear envoys last month. That meeting, held in Bali, Indonesia, on the sidelines of an Asian foreign ministers’ summit, was seen as an attempt to clear the way for broader, multinational talks on Pyongyang’s nuclear disarmament.

The United States and South Korea have said they intend to maintain dialogue with Pyongyang. But the allies are also planning to hold their latest joint military drill this month, and North Korea routinely describes such activity as grounds for invasion.