South Korean President Lee-Myung-bak is promising to take action against anyone found responsible for the fatal sinking of a naval ship near his country's maritime border with North Korea.

South Korean President Lee Myung-bak wipes away tears during the speech to his country at the presidential Blue House in Seoul on Monday. (Yonhap, Jo Bo-hee/Associated Press)In a tearful televised address Monday, Lee said South Korea will respond "resolutely and unwaveringly" to the March 26 explosion that broke the 1,200-ton Cheonan in two during a routine patrol in the Yellow Sea, killing at least 38 of the 104 sailors on board.

Officials are investigating the possibility that the ship may have been struck by a North Korean mine or torpedo.

North Korea denied any involvement Saturday and accused the South of spreading false rumours.

The two Koreas technically remain in a state of war because their 1950-53 conflict ended in a ceasefire, not a peace treaty. North Korea disputes the maritime border drawn by the United Nations at the end of the fighting.

South Korea has not accused Pyongyang of sinking the ship and Lee did not mention North Korea in his address. He pledged to build a stronger military to ensure such an incident never happens again.

"I promise you that, as president, I will uncover the cause of the Cheonan's sinking, down to the very last detail," Lee said in the 10-minute televised speech.

Wiping away tears with a handkerchief, he read out the names of all the 38 dead and eight missing sailors. The disaster is among the worst in South Korea's naval history.

"The country that you loved will never forget any of you," Lee said.

Torpedo or mine?

Speculation of North Korean involvement in the blast has mounted since the chief investigator said Friday, after an initial examination of the wreckage, that an external explosion from a torpedo or mine appeared likely. He said it was less likely that a collision or munitions stored in the warship caused the disaster.

"Both are possible, but I think the likelihood of a torpedo is more substantial," Defence Minister Kim Tae-young told legislators last week.

He also has said the ship may have been struck by a mine left over from the war, or even deliberately sent from the North. North Korea has removed some, but not all, of the 3,000 Soviet-made naval mines the regime planted in the waters off both coasts during the war, he said.

Kim has said there is no definitive evidence showing North Korea's involvement. He acknowledged during a parliamentary committee meeting Monday that survivors have testified their sonar didn't detect any signs of an approaching torpedo, there was no smell of gunpowder and columns of water were not detected at the time of the blast.

The Joint Chiefs of Staff said Monday that no shrapnel from a torpedo or a naval mine has been retrieved from the area yet.