SEOUL, South Korea -- South Korea's president said Monday his nation will no longer tolerate North Korea's "brutality" and said the regime would pay for a surprise torpedo attack that killed 46 South Korean sailors.
President Lee Myung-bak vowed to take Pyongyang to the U.N. Security Council for punishment over the March 26 sinking of the warship, suspend inter-Korean exchanges and ban North Korean ships from passing through its waters.
In a solemn address from the War Memorial, Lee cited an "incessant" pattern of attacks by communist North Korea, including the downing of an airliner in 1987 that killed 115 people. A joint international team said last week their investigation confirmed a North Korean torpedo sank South Korea's Cheonan warship on March 26.
"We have always tolerated North Korea's brutality, time and again. We did so because we have always had a genuine longing for peace on the Korean peninsula," Lee said.
"But now things are different. North Korea will pay a price corresponding to its provocative acts," he said. "I will continue to take stern measures to hold the North accountable."
The truce signed in 1953 at the close of the Korean War prevents South Korea from taking unilateral military action, and the measures laid out Monday sought to strike at impoverished, isolated North Korea diplomatically and financially.
Lee also said South Korea's military was prepared to defend itself from further provocations. The defense minister said the U.S. and South Korea would soon hold joint anti-submarine exercises.
The sinking of the Cheonan was South Korea's worst military disaster since the 1950-53 Korean War. Fifty-eight sailors were rescued from the choppy Yellow Sea waters off the Koreas' maritime border, but 46 perished.
North Korea has steadfastly denied responsibility. Naval spokesman Col. Pak In Ho warned last week in comments to broadcaster APTN that any move to retaliate or punish Pyongyang would mean war.
As Lee spoke Monday, North Korea's main newspaper, the Rodong Sinmun, called the investigation results an "intolerable, grave provocation" tantamout to a declaration of war.
"The traitor's group will not avoid our merciless punishment," the paper said in commentary carried by the official Korean Central News Agency.
The two Koreas technically remain in a state of war because the three years of fighting ended in a truce, not a peace treaty, and are divided by a heavily guarded Demilitarized Zone.
The U.N. Armistice Commission was investigating whether the sinking of the Cheonan constituted a violation of the 1953 truce.
Despite the armistice, North Korea is blamed for a number of deadly attacks on the South over the decades, including a 1983 bombing in then-Burma targeting a South Korean presidential delegation and the 1987 downing of the airliner in Burmese airspace. Burma has since renamed itself Myanmar.
The two Koreas' militaries also have clashed in the waters off the west coast.
North Korea disputes the maritime border unilaterally drawn by U.N. forces at the close of the Korean War, and the Koreas have fought three bloody skirmishes since 1999 -- most recently in November, when a gunfight killed one North Korean, according to the South Korean military.
"We ask North Korea to stop its provocative behavior," she said.
Clinton, who was due in Seoul on Wednesday, urged China to work with the United States to coordinate a response to the sinking of warship.
China, North Korea's main ally and a veto-wielding member of the U.N. Security Council, has urged restraint but has so far remained neutral on the investigation results.
Since 2006, the Security Council has issued two resolutions punishing North Korea for conducting nuclear and missile tests. Punitive measures could include more economic sanctions or condemnation of provocative acts.
Foreign Minister Yu Myung-hwan said Seoul had the support of 21 nations -- including the U.S., Japan, Britain and France -- as well as the U.N., European Union and NATO. He said Seoul has also been working with China and Russia.
Defense Minister Kim Tae-young said Seoul would resume psychological warfare against the North that had been suspended in 2004 during a period of warming relations.
Unification Minister Hyun Im-taek said Seoul would cut off all trade with North Korea apart from a joint factory park in the North Korean border town of Kaesong.
Seoul will, however, continue providing humanitarian help for infants, children and the weak, Hyun said.