The ROK's military announced provocative new artillery drills on the front-line island shelled by the Democratic People's Republic of Korea, then immediately postponed them Monday in a sign of disarray hours after the president vowed to get tough on the North. 

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Similar live-fire maneuvers by the ROK 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: the ROK 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 cancellation had nothing to do with the DPRK, and the drills will take place later, one official said. The officials spoke on condition of anonymity, citing agency rules.

Pyongyang had warned last week that it would consider any ROK drills off Yeonpyeong Island a deliberate provocation and territorial violation, and urged Seoul to call off last week's exercises. The artillery attack that came after the ROK went ahead with its drills killed four and injured 18 people.

Earlier Monday, President Lee Myung-bak gave his first address to the nation in nearly a week, 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 the ROK's response to the attack just eight months after the sinking of  the ROK warship in nearby waters that killed 46 sailors.

Hours after his speech, authorities on Yeonpyeong (yuhn-pyuhng) announced new live-fire drills for Tuesday morning, warning residents by loudspeaker to take shelter in underground bunkers well in advance. Another announcement later in the evening said there would be no exercise.

Meanwhile, a nuclear-powered US supercarrier and a the ROK 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 off an aircraft carrier as part of drills to practice air defense, combat warfare and search-and-seizure drills, said Rear Adm. Dan Cloyd, commander of the USS George Washington Carrier Strike Group.

Lee observed the drills Monday from the US Army's command center in Seoul, along with Gen. Walter Sharp, the top commander in the ROK, in a pointed show of unity.

"This exercise demonstrates our interoperability and how closely integrated the ROK-US forces are along with the capability both bring in defense of the peninsula that is the cornerstone of regional stability," Sharp said in a statement posted by the military.

Amid the heightened tension, classified US State Department documents leaked Sunday by online whistle-blower WikiLeaks showed the United States and the ROK 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 on Monday.