Seoul - North Korea fired more than 100 artillery rounds into South Korean waters as part of a drill on Monday, prompting the South to fire back, officials in Seoul said, but the exercise appeared to be more sabre-rattling from Pyongyang rather than the start of a military standoff.
The North had flagged its intentions to conduct the exercise in response to UN condemnation of last week's missile launches by Pyongyang and against what it says are threatening military drills in the South by US forces.
North Korea also accused the South of "gangster-like" behaviour at the weekend by "abducting" one of its fishing boats and threatened to retaliate. The South said it had sent the boat back after it drifted into its waters.
More than 100 North Korean shells out of 500 or so fired landed in South Korean waters, prompting marines from the South to fire back with more than 300 rounds into the North's waters, defence officials in Seoul said.
Seoul also scrambled F-15s on its side of the maritime border, they said.
"We believe the North's maritime firing is a planned provocation and an attempt to test our military's determination to defend the Northern Limit Line and to get an upper hand in South-North relations," South Korean Defence Ministry spokesperson Kim Min-seok said.
In Washington, the White House called North Korea's actions "dangerous and provocative" and said the country's threats and provocations only isolate it further.
"We remain steadfast in our commitment [to] the defence of our allies and remain in close coordination with both the Republic of Korea and Japan," White House National Security Council spokesperson Jonathan Lalley said.
The Northern Limit Line, a maritime border that wraps itself around a part of the North's coastline, has been the scene of frequent clashes and in 2010, four people were killed when North Korea shelled the South Korean island of Yeonpyeong.
"It's up to the two militaries either to recognise or reject their own claimed line, and challenge the others. This goes back and forth, so this is probably another episode of that," said Daniel Pinkston of the International Crisis Group.
Earlier in 2010, a South Korean naval vessel was sunk close to the line by what an international commission said was a North Korean torpedo, although the North denies involvement.
The line was drawn up at the end of the 1950-53 Korean War and North Korea does not recognise it. The two sides are still technically at war as the conflict ended in a mere truce, not a treaty.
The residents of Baengnyeong island, one of the remote islands close to the firing area, were evacuated to bomb shelters as a precaution, a government official said by telephone.