A U.S. aircraft carrier group set off for Korean waters on Wednesday, a day after North Korea launched artillery shells on a South Korean island, a move likely to enrage Pyongyang and unsettle its ally, China.
The nuclear-powered USS George Washington, which carries 75 warplanes and has a crew of over 6,000, left a naval base south of Tokyo and would join exercises with South Korea from Sunday to the following Wednesday, U.S. officials in Seoul said.
"This exercise is defensive in nature," U.S. Forces Korea said in a statement. "While planned well before yesterday's unprovoked artillery attack, it demonstrates the strength of the ROK (South Korea)-U.S. alliance and our commitment to regional stability through deterrence."
The move appeared aimed at reinforcing heavy pressure on China to rein in North Korea after the reclusive nation fired dozens of artillery shells at the South Korean island. Two South Korean soldiers were killed and houses set ablaze in the heaviest attack in the region since the Korean War ended in 1953.
Pyongyang said the firing was in reaction to military drills conducted by South Korea in the area at the time but Seoul said it had not been firing at the North.
U.S. President Barack Obama, woken up in the early hours to be told of the artillery strike, said he was outraged and pressed the North to stop its provocative actions.
Although U.S. officials said the joint exercise was scheduled before the attack by North Korea, it was reminiscent of a crisis in 1996 when then President Bill Clinton sent an aircraft carrier group through the Taiwan Strait after Beijing test-fired missiles into the channel between the mainland and Taiwan.
Tuesday's bombardment nagged at global markets, already unsettled by worries over Ireland's debt problem and looking to invest in less risky assets.
But South Korea's markets, after sharp falls, recovered lost ground.
"SEMI STATE OF WAR"
"If you look back at the last five years when we've had scares, they were all seen as buying opportunities. The rule among hedge funds and long-only funds is that you let the market sell off and watch for your entry point to get involved," said Todd Martin, Asia equity strategist with Societe Generale in Hong Kong.
"We're in a semi state of war," South Korean coastguard Kim Dong-jin told Reuters in the port city of Incheon where many residents of Yeonpyeong island fled in panic as the bombardment triggered a fire storm.
Despite the rhetoric, regional powers made clear they were looking for a diplomatic way to calm things down.
South Korea, its armed forces technically superior though about half the size of the North's one-million-plus army, warned of "massive retaliation" if its neighbour attacked again.
But it was careful to avoid any immediate threat of retaliation which might spark an escalation of fighting across the Cold War's last frontier.
Japanese Prime Minister Naoto Kan called on China to help rein in the hermit state.
China has long propped up the Pyongyang leadership, worried that a collapse of the North could bring instability to its own borders and also wary of a unified Korea that would be dominated by the United States, the key ally of the South.
A number of analysts suspect that Tuesday's attack may have been an attempt by North Korean leader Kim jong-il to raise his bargaining position ahead of disarmament talks which he has used in the past to win concessions and aid from the outside world, in particular the United States.
"It's Mr Kim's old game to get some attention and some economic goodies," said Lin Chong-pin, strategic studies professor at Tamkang University in Taipei.
Several analysts believe the attacks may also have been driven by domestic politics, with the ailing Kim desperate to give a lift to his youngest son, named as heir apparent to the family dynasty in September but who has little clear support in the military.
