By Na Jeong-ju
Staff reporter

President Lee Myung-bak will convene a meeting of the National Security Council (NSC) today to discuss stern countermeasures against North Korea for its torpedo attack on the Navy vessel Cheonan on March 26, Cheong Wa Dae said Thursday.

The announcement came immediately after an international team of investigators revealed the wreckage of the North Korean-made torpedo they had collected from the sea bed near where the ship sank, saying they had concluded the communist nation was behind the disaster.

"The NSC will focus on a joint international response to the act of aggression and enhancing defense readiness on the inter-Korean border," said Lee Dong-kwan, senior presidential secretary for public relations.

"Watching the team's press conference on television, the President showed little emotion, but he looked grim and resolute."

Earlier in the day, Lee called Australian Prime Minister Kevin Rudd to discuss Seoul's plan to take Pyongyang to the U.N. Security Council for diplomatic and military sanctions over the sinking.

Rudd became the latest foreign leader to express full support for South Korea in seeking a joint international response to the naval tragedy, following U.S. President Barack Obama and Japanese Prime Minister Yukio Hatoyama, the presidential office said.

President Lee plans to speak to the nation Monday to call for national unity.

"In the nationally-televised address, Lee will present various measures the government will take to punish North Korea," said presidential spokesman Park Sun-kyoo.

The military called an emergency meeting of Army, Navy and Air Force commanders in the afternoon to discuss the situation in North Korea and strengthen surveillance at the border.

South Korea, the United States and Japan, using the evidence of a torpedo attack, are stepping up diplomacy with China and Russia, the North's main allies, to persuade them into joining any counteraction.

U.S. Secretary of State Hillary Clinton will visit Tokyo Friday to discuss security issues with Japanese diplomats before flying to China, where she will attend the annual strategic dialogue between Washington and Beijing. She will visit Seoul on May 26 on her way back home from Beijing.