SEOUL, South Korea – South Korea’s foreign minister said Wednesday it was “obvious” that North Korea fired a torpedo that sank one of the South’s warships in March, killing 46 sailors.

Foreign Minister Yu Myung-hwan told reporters that investigators have enough evidence of North Korean involvement in the sinking of the Cheonan to warrant taking Pyongyang to the U.N. Security Council and would be presenting their findings Thursday.

Yu’s comments are the first by a South Korean official clearly pointing the finger at North Korea for one of the worst attacks on the South since the two Koreas signed a truce in 1953 to end three years of fighting.

A thorough and exhaustive investigation revealed that a “strong underwater explosion generated by the detonation of a torpedo caused the Korean battleship to split apart and sink,” he said in a speech to Seoul-based European business executives.

Asked later by reporters if North Korea sank the ship, Yu said: “I think it’s obvious.” He declined to provide further details, saying the official results of the multinational investigation into the incident would be released Thursday.

North Korea has denied involvement in the sinking of the Cheonan near the Koreas’ maritime border on March 26. Vice parliamentary speaker Yang Hyong Sop criticized Seoul for “unreasonably” linking Pyongyang to the sinking earlier this week, according to Pyongyang’s state radio station.

However, investigators will lay out evidence showing that a North Korean torpedo attack triggered the explosion that sank the Cheonan near the Koreas’ tense western sea border, a U.S. official said in Washington, speaking on condition of anonymity.and

Investigators have collected damning evidence pointing to Pyongyang’s involvement in the blast that blew the 1,200-ton warship apart during a routine patrolling mission in the Yellow Sea, local media said. Fifty-eight sailors were rescued; 46 died.

Fragments of a torpedo propeller found near the disaster site are similar to parts from a North Korean torpedo that South Korea obtained seven years ago, the Chosun Ilbo newspaper reported Wednesday, citing unidentified government officials.

A serial number on the torpedo propeller was written in a font typically used in North Korea, and traces of explosives found in the wreckage resemble the gunpowder used in the North Korean torpedo retrieved in 2003, the paper said.

The Dong-a Ilbo newspaper carried a similar report, saying an 85-ton North Korean submersible is believed to have torpedoed the vessel. Citing an unidentified government official, the report said the conclusion was based on intelligence on the movement of North Korean submersibles and analyses of intercepted North Korean military communication.

South Korea’s Defense Ministry said it could not confirm the reports.

Diplomatic discussions were already under way Wednesday in Seoul and in Washington.

U.S. Secretary of State Hillary Rodham Clinton met privately late Tuesday with envoys Stephen Bosworth and Sung Kim, while South Korea’s Foreign Ministry briefed foreign ambassadors in Seoul on Wednesday.

President Lee Myung-bak has vowed stern action against the culprits. He discussed the matter with President Barack Obama by phone Monday, officials said.

Yu called for “firm” action and pushed for support from the international community during the speech.

The investigation results and concerns about North Korea’s nuclear program are expected to dominate Clinton’s talks this week and next with leaders in Tokyo, Beijing and Seoul, where she will finish her Asian trip next Wednesday.

The two Koreas remain locked in a state of war and divided by the world’s most heavily guarded border because their three-year conflict ended in a truce, not a peace treaty, in 1953.

However, North Korea disputes the maritime border drawn by the U.N. in 1953, and the western waters have been the site of several deadly naval clashes since 1999.

In Washington, State Department spokesman P.J. Crowley said North Korea must “cease provocative acts, cease acts of aggression that destabilize the region” and urged the North to follow through on past commitments to abandon its nuclear programs.

The United States had pushed the North to return to stalled six-nation nuclear disarmament talks, but U.S. officials have said the findings of the ship sinking investigation will be a major factor in whether those talks resume. — AP

(This version CORRECTS UPDATES with quotes, corrects death toll.)