North Korea on Thursday called South Korea’s claim of an artillery exchange between the rivals “preposterous,” saying a frightened South mistook construction noise for artillery when it accused Pyongyang of opening fire near the rivals’ disputed maritime line.

North Korea said in a statement that the South overreacted to “normal blasting” from a North Korean construction project “aimed at improving the standard of people’s living.” South Korean defense officials say marines returned fire Wednesday after North Korea launched artillery shells into the same waters that saw a deadly artillery exchange between the countries last November.

“It was preposterous in the age of science when latest detecting and intelligence means are available that they mistook the blasting for shelling,” an unnamed North Korean representative to inter-Korean military talk said in a statement released by the official Korean Central News Agency. “It was a tragicomedy that they indiscriminately reacted to what happened with counter-shelling even without confirming the truth about the case in the sensitive waters.”

South Korean Defense Ministry spokesman Kim Min-seok said three North Korean shells originally fired near the Northern Limit Line in the Yellow Sea prompted the South to fire three shells back. Another ministry official, who refused to be named because of office policy, said North Korea fired more rounds later in the day and that South Korea responded.

All the shells landed in the water, South Korea said, and there were no reports of casualties.

South Korean forces have been on high alert in the area since a North Korean artillery attack killed four people, including two marines, in November on South Korea’s Yeonpyeong island. Wednesday’s artillery exchange was near that island, South Korea said.

It follows a recent easing of animosity between the Koreas and comes ahead of joint U.S.-South Korean military drills set for next week. Last month, a senior North Korean diplomat met with U.S. officials in New York to negotiate ways to restart long-stalled international talks aimed at persuading the North to abandon its nuclear weapons aspirations. The meeting came after the Koreas’ nuclear envoys held cordial talks during a regional security forum in Indonesia.

In its statement Thursday, the North repeated its call for the cancellation of the U.S.-South Korean drills and said South Korea was deliberately trying to ruin “the atmosphere of dialogue in the Korean peninsula.”

On Wednesday, the United States urged North Korea to exercise restraint and take steps to allow the six-nation disarmament talks to resume.

“This incident is now over, and we now need to move back to the main business at hand,” State Department spokeswoman Victoria Nuland told reporters in Washington.

The North’s shelling took place unexpectedly, South Korean officials said, and neither side was conducting firing drills at the time.

Violence often erupts in the contested slice of sea. Three deadly naval clashes since 1999 have taken a few dozen lives.

Kim said one North Korean artillery shell is believed to have fallen south of the maritime line.

The maritime line separating the countries was drawn by the U.S.-led U.N. Command without Pyongyang’s consent at the close of the 1950-53 Korean War, which ended with a truce, not a peace treaty, leaving the peninsula still technically in a state of war. North Korea routinely argues that the line should run farther south.

Baek Seung-joo, a military analyst at the state-run Korea Institute for Defense Analyses in South Korea, said the North appears to be rattling its sabers ahead of the annual U.S.-South Korean military exercises.

On Monday, a North Korean military spokesman released an open letter that called the joint exercises “hideous provocations.” He warned that the North has access to a “nuclear deterrent powerful enough to protect” itself.

The North has conducted two nuclear tests since 2006.

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