SEOUL, South Korea — In an emotional speech televised live to a grieving nation, South Korean PresidentLee Myung-bak on Monday vowed to pursue those responsible for last month’s deadly sinking of a naval warship.

Without mentioning North Korea, the conservative leader, elected in 2008 on a promise to challengeKim Jong-il’s regime, said he would “”resolutely and unwaveringly cope with the results”” of the investigation into one of South Korea’s worst naval disasters.

Pledging to make South Korea’s military stronger to prevent a similar episode, Lee broke into tears as he read the names of 46 crewmen who died when the Cheonan sank following a mysterious nighttime explosion.

The March 26 blast broke the 1,200-ton corvette in two as it patrolled near the contested sea border between North and South. South Korean officials have said they have not ruled out a possibility that the vessel was downed by a naval mine or torpedo.

The leader of the probe, which includes experts from several countries including the U.S., believes the cause was external, rather than exploding ammunition aboard ship.

North Korea on Saturday responded angrily to suggestions it was responsible for the disaster, accusing Seoul of spreading false rumors for political gain before upcoming elections.

On Sunday, however, South Korean officials suggested they would take the matter to the U.N. Security Council if the probe determined North Korean involvement.

South Korean Defense MinisterKim Tae-young on Monday turned up the heat on Pyongyang, telling a parliamentary hearing that the South Korean military had “”judged that it was North Korea’s act as soon as the incident occurred.””

Wearing a black suit and tie, an emotional Lee for the first time addressed the nation on TV over the Cheonan’s sinking. Previously he had spoken about the sinking during his regular radio addresses and has flown to the scene to console family members of crewmen.

“”I promise you that as the president I will uncover all details of the cause of the Cheonan’s sinking to the end,”” he said in a 10-minute speech, later adding. “”I will make the military stronger.””

Fifty-eight crewmen, including the captain, were rescued as the ship sank. In the ensuing weeks, 38 bodies have been found, most of them last week when the vessel’s stern was raised from the water. Eight crew members remain unaccounted for.

One South Korean newspaper reported on Monday that a senior U.S. intelligence official had visited Seoul earlier this month to help determine whether North Korea had engaged in any suspicious activity around the time of the Cheonan’s sinking.

During his speech, Lee wept as he read the names of the dead and missing crewmen. “”Your fatherland, which you loved,”” he said, his voice breaking, “”will not forget you, ever.””

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(Researcher Ju-min Park contributed to this report.)