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US warns North Korea for firing into South’s waters

US and South Korean forces on Monday participated in joint military exercises, which the North sees as a threat.

Jeon Heon Kyun/European Pressphoto Agency

US and South Korean forces on Monday participated in joint military exercises, which the North sees as a threat.

SEOUL — The United States warned North Korea on Monday that its decision fire artillery rounds into South Korean waters was a dangerous step that would further aggravate tensions in the region.

North and South Korea fired hundreds of artillery shells into each other’s waters early Monday in a flare-up of animosity that forced residents of five front-line South Korean islands to move to shelters for several hours, South Korean officials said.

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White House spokesman Jonathan Lalley called North Korea’s actions ‘‘dangerous and provocative.’’

Lalley said the aggression will only deepen North Korea’s isolation. He said the United States remains steadfast in its commitment to the defense of its allies and is working in close coordination with South Korea and Japan.

Monday’s exchange was relatively mild in the history of animosity and violence between the Koreas, but there is worry in Seoul that an increasingly dissatisfied North Korea could repeat the near-daily barrage of war rhetoric it carried out last spring, when tensions soared as Pyongyang threatened nuclear strikes on Washington and Seoul in response to condemnation of its third nuclear test.

The exchange of fire into the Yellow Sea followed Pyongyang’s sudden announcement that it would conduct live-fire drills in seven areas north of the Koreas’ disputed maritime boundary. North Korea routinely test-fires artillery and missiles into the ocean but rarely discloses those plans in advance.

The announcement was seen as an expression of Pyongyang’s frustration at making little progress in its recent push to win outside aid.

North Korea fired 500 rounds of artillery shells over more than three hours, about 100 of which fell south of the sea boundary, South Korean Defense Ministry spokesman Kim Min Seok said. South Korea responded by firing 300 shells into North Korean waters, he said.

No shells from either side were fired at land or military installations, but Kim called the North’s artillery firing a provocation aimed at testing Seoul’s security posture. There was no immediate comment from North Korea.

Residents on front-line South Korean islands spent several hours in shelters during the firing, and officials temporarily halted ferry service linking the islands to the mainland.

The poorly marked western sea boundary has been the scene of several bloody naval skirmishes between the Koreas in recent years. In March 2010, a South Korean warship sank in the area following a torpedo attack blamed on Pyongyang that left 46 sailors dead.

North Korea denies responsibility for the sinking. In November 2010, a North Korean artillery bombardment killed four South Koreans on Yeonpyeong.

The North calls the ongoingSouth Korea-US springtime military exercises a rehearsal for invasion; the allies say they the drills are routine and defensive.

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