Tensions heightened in the Asia Pacific as North Korea fired more artillery shells within earshot of South Korea's Yeongpyeong Island, even as it warned that joint U.S.-South Korean military exercises could put the region on the brink of war.
China also expressed similar concerns about upcoming military drills before the scheduled weekend arrival of U.S. aircraft carrier USS George Washington.
The joint exercises in the Yellow Sea had been scheduled before tensions erupted in the region this week, and the U.S. administration vowed to go forward with them, even raising the possibility of conducting more exercises.
Gen. Walter Sharp, the U.S. commander in South Korea, toured Yeongpyeong Island Friday in a show of support as U.S. allies such as Japan denounced the North Korean attack, calling it "intolerable."
South Korean officials today blamed their neighbors for firing artilleries to "intentionally increase tensions," and the government canceled an aid shipment to the north that was about to be delivered from northern China.
South Korean President Lee Myung-bak ordered more troops and advanced weaponry to the maritime border with North Korea, including the island that was hit, warning that another attack could be imminent. He called for more aggressive rules of engagement.
South Korea's defense minister resigned Thursday after what many said was too slow of a response to North Korean's firing. New defense minister Kim Kwang-Jin, a former chairman of the Joint Chiefs of Staff, vowed to "reform" and "strengthen" the military in a direct response to civilians who, while used to North Korean provocations, now feel it is time to go tough on their neighbor.
North Korea, in the meantime, upped its threats, saying it would respond to confrontation with more attacks. The state media called South Korean president Lee Myung-bak a "puppet" and charged that it would be naive to even consider holding a dialogue with him.
"Escalated confrontation would lead to a war, and he who is fond of playing with fire is bound to perish therein. Gone are the days when verbal warnings are served only," a newsreader for North Korean state TV KRT said in a report. "We will respond to good faith in kind but punish the provocateurs encroaching upon our dignity and sovereignty with resolute and merciless counter-action." Skirmishes between the two countries began Tuesday, when North Korea fired artillery shells at South Korea's Yeonpyeong Island, killing two civilians and two marines. North Koreans charge that training exercises in the region spurred the attack, and that its neighbor fired into its territorial water during military exercises, while South Korea argued that the drills were routine.
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The western sea border has been at the center of dispute where the two Koreas have fought bloody skirmishes, most recently in November 2009. North Korea does not recognize the maritime border set by the United Nations in 1953, and considers the waters around Yeonpyeong island its territory.
But this marked the first time since the end of the Korean War, in 1953, that North Korea fired on South Korea's civilian territory, triggering a similar response from Seoul.
The chairman of the Joint Chiefs of Staff, Mike Mullen, said Wednesday that the North Korean provocation may be linked to the succession of power from Kim Jong Il to his 27-year-old son, Kim Jong Un.
He said the situation is worrying, even more so because North Korea proved last week that it was not backing down from its nuclear ambitions.
This week President Obama called on China, Pyongyang's biggest ally in the region, to "make clear to North Korea that there are a set of international rules that they need to abide by." But response from Beijing so far has been relatively meek.
The Chinese government called for calm and restraint in a statement but mostly expressed concern about military exercises in the Yellow Sea.
ABC News' Joohee Cho, Alex Marquadt, Jessica Hopper and The Associated Press contributed to this report.