In a drill that was obviously construed as hostile, North Korea fired hundreds of artillery shells into South Korean waters on Monday, which resulted in a bit of a flare-up by South Korea, causing residents of the South Korean islands to evacuate the area for several hours, South Korean officials said.

South Korea says it returned fire after North Korean shells landed in its territorial waters.

The area of water in question has been a trouble spot between the two Koreas. Although the UN drew the western border area after the Korean War, North Korea has never recognized it.

The return fire could have occurred because of a border fire in 2010 that killed four South Koreans by North Korean artillery fire.

The North had indicated to the South that they intended to conduct the firing exercises, announced in a faxed message to the South’s navy. The exercises, which were in response to the U.N. condemnation of its missile launches by Pyongyang, were against what it says are threatening military drills in the South by U.S. forces.

North Korea has now accused the South of “gangster-like” behavior at the reaction they displayed 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, defense 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 Defense Ministry spokesman Kim Min-seok said.

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 defense of our allies and remain in close coordination with both the Republic of Korea and Japan,” White House National Security Council spokesman Jonathan Lalley said.

United States Defense Secretary Chuck Hagel said he would raise U.S. concerns about the North’s behavior during a trip to China next week. “The North Koreans have to stop these provocative actions,” he told reporters. “Obviously when I’m in China that will be a subject that I will discuss with my counterpart.”

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