APTN, Associated Press
Ctizens attend a rally in support of North Korea's "joint new year editorial" in the city's central Kim Il Sung Square, in Pyongyang, North Korea Monday, Jan. 3, 2011. In the North Korean capital, tens of thousands gathered Monday for the annual New Year rally to display loyalty to leader Kim Jong Il.

SEOUL, South Korea (AP) — South Korea's president said Monday that his country has no choice but to aggressively boost its defenses after a deadly North Korean artillery attack, vowing not to let the North "covet even an inch of our territory."

Lee Myung-bak, speaking to the country in a New Year's speech, said the South must treat the Nov. 23 shelling of Yeonpyeong Island as the United States treated the September 11, 2001, terrorist attacks and "overhaul our defense posture."

"Peace cannot be obtained without a price," Lee said. "Any provocation that would pose a threat to our lives and property will not be tolerated. Such provocations will be met with stern, strong responses."

Lee was severely criticized after the North's artillery attack for responding too slowly and too weakly. His government has responded by replacing the defense chief and strengthening security and pushing to deploy additional troops and weaponry to Yeonpyeong, which lies just seven miles (11 kilometers) from North Korean shores.

Four South Koreans, including two civilians, were killed in the shelling, which North Korea carried out after warning Seoul against conducting live-fire drills there. The attack was the first on a civilian area since the 1950-53 Korean War.

North Korea does not recognize the maritime border drawn by the U.N. in 1953, and it claims the waters around the island as its own. The Korean peninsula remains technically in a state of war because the conflict ended in a truce, not a peace treaty.