South Korean President Lee Myung-bak promised "stern action" against North Korea on Thursday after a multinational group of investigators found concrete evidence linking the North to the sinking of his country's warship in March.
An investigation into the March 26 sinking of the Cheonan turned up two key pieces of evidence — traces of explosives and part of a propeller — linked to North Korea.
U.S. and East Asian officials, speaking on background due to the highly sensitive nature of the investigation, said TNT found at the site has been identified as identical to explosives in a North Korean torpedo that South Korea recovered from its southern coast seven years ago.
Investigators also found that Korea's Hangul script was used in the serial number engraved on the torpedo propeller, the officials said.
"The evidence points overwhelmingly to the conclusion that the torpedo was fired by a North Korean submarine," the multinational team said in its report, according to an Agence France-Presse dispatch. "There is no other plausible explanation."
The report said torpedo parts salvaged from the site of the Cheonan sinking "perfectly match the schematics of the CHT-02D torpedo included in introductory brochures provided to foreign countries by North Korea for export purposes."
Investigators from South Korea, the U.S., Britain, Australia, Canada and Sweden probed the Cheonan sinking.
Kurt Campbell, assistant secretary of state for East Asian and Pacific affairs, told reporters Wednesday the U.S. has been "deeply and actively involved in all aspects of the investigation and the United States strongly supports its conclusions."
The Cheonan sank after an explosion in the Yellow Sea off South Korea's west coast.
North Korea on Thursday denied responsibility and warned of "full-scale war" if new sanctions are imposed, according to Seoul's Yonhap news agency.
Analysts said the findings diminish any hope of a resumption of six-party talks to denuclearize North Korea and will pressure China to support sanctions on Pyongyang, with which it shares cordial relations.
Besides the two Koreas, the U.S., Russia, China and Japan are part of the stalled six-party talks.
Jae Ku, director of the U.S.-Korea Institute at Johns Hopkins University's School of Advanced International Studies, said there was enough forensic evidence to tie North Korea to the sinking of the Cheonan.
"This is a pretty clear-cut case that the ship was hit by a torpedo. There is forensic evidence that it was a North Korean torpedo," Mr. Ku said.
Bruce Bechtol, a professor of international relations at the Marine Corps University's Command and Staff College in Quantico, Va., said the torpedo used in the incident was a Yu-3, originally manufactured by China.
Explaining why the propeller would be engraved in Hangul, he said it was likely that North Korea acquired the design of this torpedo from China and then copied it to make its own.
While sources point to evidence of a North Korean link to the torpedo, they said it was not clear from what platform it had been fired.
Mr. Bechtol said the North Koreans might have used a Sang-O class or a smaller Yugo submarine to fire the torpedo. He said it was unlikely that a semisubmersible platform had been used since the waters in which the incident took place are extremely choppy.
Citing preliminary intelligence assessments, The Washington Times reported earlier this month that the planning for the operation to sink the Cheonan began late last year and included North Korean navy exercises with special operations forces that ultimately were used in the attack.
Additionally, senior North Korean military officials, including the chief of the general staff in Pyongyang, were suspected of involvement.
There was also indication of involvement by a three-star general, Kim Myong-guk, who had been demoted from four-star rank after a North-South naval clash in November. The general recently appeared in a photograph in the North Korean state-run press as having regained his fourth star after the sinking.
Sources said the release of the Cheonan report was brought forward to coincide with Secretary of State Hillary Rodham Clinton's visit to the region. Mrs. Clinton leaves for Japan, China and South Korea on Thursday. She will discuss the Cheonan incident in her meetings in Seoul on May 26.
Kim Kwang-jin, who worked in the financial sector in North Korea before defecting in 2003, said North Korea's role in the Cheonan incident proves that "there was no strategic change in North Korea's policy toward South Korea and also toward the security issue in the Korean Peninsula."
In an interview with The Times, Mr. Kim said the people of North Korea had been brainwashed and fed propaganda from the regime in Pyongyang about the incident. "They will never openly say they [sank the Cheonan]," he said of the North Korean leadership.
He was skeptical about the effectiveness of the international approach toward North Korea. But "we can at least make them pay for what they have done the instability in the peninsula and the bad things they have done to their own people," he added.
Analysts and officials say a military response to the incident is unlikely.
"The big dilemma for South Korea is 'How do you respond to North Korea's bad behavior?'" Mr. Ku said.
He warned that a military response would further escalate tensions in the region. The North and South remain technically at war under a truce that ended fighting in the 1950-53 Korean War.
South Korea and the international community are left with the option of approaching the U.N. Security Council for a fresh round of sanctions on North Korea. Analysts said this approach would put China in a spot, since Beijing would be reluctant to support sanctions against North Korean leader Kim Jong-il, whom it hosted this month on his first visit to China since 2004, because it would be directly affected by instability in North Korea.
"The Chinese would not go along with sanctions enforcement. It is wishful thinking to keep talking about a responsible response from China," said Mr. Ku.
He said the incident also will put pressure on the U.S. to rethink the effectiveness of six-party talks.