ABOARD USS GEORGE WASHINGTON (AP) - U.S. and South Korean warships and helicopters staged anti-submarine maneuvers off the Korean peninsula Monday meant as a warning to Pyongyang that aggression in the region will not be tolerated.
An international investigation blamed the North for the sinking of a South Korean warship that killed 46 sailors in what officials called the worst military attack on the South since the 1950-53 Korean War.
The four-day "Invincible Spirit" exercises involving 20 ships, 200 aircraft and about 8,000 U.S. and South Korean sailors off South Korea's east coast drew threats of retaliation from North Korea, which denies responsibility for the attack on the Cheonan.
Over the East Sea, a formation of fighter jets buzzed across the skies in a thundering wave as a helicopter hovered near a South Korean naval ship. Other aircraft practiced refueling midair.
The anti-submarine phase of the training - which also involves anti-ship and anti-aircraft operations - is particularly important because investigators found that a torpedo launched from a North Korean submarine sank the 1,200-ton Cheonan, somehow penetrating South Korea's defenses.
"North Korea's danger lies because they are unpredictable," said Capt. David Lausman, the commanding officer of the USS George Washington, a nuclear-powered supercarrier deployed to the maneuvers from its home port in Japan.
"The sinking of the Cheonan is a prime example." Pyongyang has strongly protested the exercises, calling them a provocation and threatening retaliation. In flourishes of rhetoric typical of the regime, it vowed to respond with a "sacred war" and a "powerful nuclear deterrence."
"Should the U.S. imperialists and (South Korea) finally ignite a new war of aggression ... (North Korea) will mobilize the tremendous military potential including its nuclear deterrence for self-defense and thus wipe out the aggressors," North Korea's defense chief, Kim Yong Chun, said in Pyongyang on Monday, according to the official Korean Central News Agency.
Kim also reiterated the country's threat to bolster its nuclear deterrence. North Korea often cites the U.S. military presence in the region, with nuclear-powered warships like the George Washington, as a key reason behind its drive to build atomic weapons.
Pyongyang's latest rhetoric was seen by most as bluster: South Korea's Defense Ministry reported no significant moves by the North Korean military since the maneuvers began Sunday. But the threats carry extra weight following the sinking of the Cheonan, which dramatically intensified tensions on the Korean peninsula.
The ship sank near the Koreas' western sea border, a scene of three bloody inter-Korean maritime battles in the past decade, most recently in November. U.S. officials say that the maneuvers, held well away from North Korea's border, are not intended to provoke a response, but add that they want to send Pyongyang a message that further aggression in the region will not be tolerated.
Cmdr. Ray Hesser, head of an anti-submarine helicopter squadron on the George Washington, said North Korean submarines are largely restricted to shallow, coastal waters. "We're not expecting to see them out here," he said.
"I would not think they would be willing or wanting to come all the way out here." He said the attack on the Cheonan probably came when the South Korean warship was not prepared, noting that U.S. ships observe higher readiness. The maneuvers underscore a diplomatic blitz by the United States aimed at further tightening the screws on North Korea.
U.S. Secretary of State Hillary Rodham Clinton announced during a visit to Seoul last week that the U.S. would slap new sanctions on the North to stifle its nuclear ambitions and punish it for the Cheonan sinking. The European Union is also considering new sanctions on North Korea. --- Associated Press writer Hyung-jin Kim in Seoul contributed to this report.