South Korea cancels new artillery drill on tense island

South Korea's military announced provocative new artillery drills on the front-line island shelled in a deadly North Korean attack, then immediately postponed them Monday in a sign of disarray hours after the president vowed to get tough on the North.

Similar live-fire maneuvers by South Korean troops one week earlier triggered the North's bombardment that decimated parts of Yeonpyeong Island, killed four people and drew return fire in a clash that set the region on edge.

The new drills originally planned for Tuesday could have had even higher stakes: South Korean and American warships are currently engaged in separate military exercises in waters to the south.

Officials at the Joint Chiefs of Staff told The Associated Press on Monday that the latest drills were postponed after the marine unit on the island mistakenly announced them without getting final approval from higher military authorities. The cancelation had nothing to do with North Korea, and the drills will take place later, one official said. The officials spoke on condition of , citing agency rules.

Earlier Monday, President Lee Myung-bak gave his first address to the nation since the attack, taking responsibility for failing to protect his citizens, expressing outrage at the North's "ruthlessness" and vowing tough consequences for any future aggression.

Lee has come under withering criticism for what opponents have called lapses in South Korea's response to the attack just eight months after the sinking of a South Korean warship in nearby waters.

On Yeonpyeong island after the speech, authorities announced new live-fire drills for Tuesday morning, and issued a warning over loudspeakers for residents to take shelter in underground bunkers. Hours later, another announcement over the loudspeakers said there would be no live-fire exercise.

The North's artillery attack last week also wounded 18 people on an island that lies within sight of North Korean shores. North Korea had called the drills a violation of its territorial waters and a deliberate provocation after Pyongyang urged South Korean officials not to carry out the exercises, and has warned of a "merciless" attack if further provoked.

Meanwhile, a nuclear-powered U.S. supercarrier and a South Korean destroyer carried out joint military exercises in the waters south of the island in a united show of force by the longtime allies. Jets roared as they took off from the carrier.

Amid the heightened tension, classified U.S. State Department documents leaked Sunday by online whistle-blower WikiLeaks showed the United States and South Korea discussing possible scenarios for reunification of the peninsula, and American worry over Pyongyang's nuclear weapons program.

Under pressure to take stronger action in dealing with the defiant North, Lee lashed out at Pyongyang.

"Only a few meters away from where shells landed, there is a school where classes were going on," Lee said. "I am outraged by the ruthlessness of the North Korean regime, which is even indifferent to the lives of little children."

In the past week, Lee has replaced his defense minister, ordered reinforcements for the 4,000 troops on Yeonpyeong and four other Yellow Sea islands, and upgraded the military rules of engagement.

"If the North commits any additional provocations against the South, we will make sure that it pays a dear price without fail," Lee warned.

He didn't offer specifics about what consequences the North would face, and he offered few details on what actions South Korea will take in response to last week's attack, other than promising to strengthen the military.

On Yeonpyeong, the military has added long-range artillery guns, doubling the amount of K-9 howitzers to 12, and multiple rocket launchers, the Yonhap news agency reported, citing unnamed military officials.

Minutes after the speech, North Korea issued another threat to attack South Korea and the United States, calling the allies' joint war drills "yet another grave military provocation."

The two Koreas are required to abide by an armistice signed in 1953 at the close of their brutal, three-year war.

However, North Korea does not recognize the maritime border drawn by the U.N. at the close of the war, and considers the waters around Yeonpyeong Island its territory.

The waters have been the site of three deadly skirmishes since 1999, as well as the sinking of the Cheonan warship in March that killed 46 sailors and last week's artillery attack.

Yeonpyeong Island, normally home to about 1,300 civilian residents, was declared a special security area Monday, which could pave the way for a forced evacuation the 300 residents, journalists and officials still left on the island.

Military trucks carrying what appeared to be multiple rocket launchers were seen heading to a marine base on the island Monday.

China, North Korea's only major ally, has sought to calm tensions.

Beijing's top nuclear envoy, Wu Dawei, called Sunday for an emergency meeting in early December among regional powers involved in nuclear disarmament talks, including North Korea.

Seoul, which wants proof of Pyongyang's commitment to denuclearization as well as a show of regret over the Cheonan incident, gave a cool response to the proposal.

Japan's Prime Minister Naoto Kan again condemned North Korea's deadly artillery barrage Monday, calling the attack on civilians "a barbaric act." He said Tokyo would cooperate with Seoul and Washington on how to counter North Korea's "reckless" acts.

The documents leaked by WikiLeaks showed deep U.S. worries about North Korean and Iranian cooperation on their rogue nuclear programs.

The New York Times published documents that indicated the United States and South Korea were "gaming out an eventual collapse of North Korea" and discussing the prospects for a unified country, if the North's economic troubles and political transition lead it to implode.