SEOUL, South Korea — Torpedo fragments, blast patterns and testimony from survivors all point to North Korea as the culprit in a brazen March 26 attack that sank a South Korean patrol ship, a multi-national team of investigators announced Thursday.

“There is no other plausible explanation,” said Yoon Duk-yong, co-chair of the team that studied the explosion that killed 46 of 104 sailors on board the Cheonan as it patrolled the Yellow Sea near the maritime border between the two Koreas.

Investigators said a 130-ton “midget” North Korean submarine equipped with night vision capabilities entered the Yellow Sea undetected during the night of March 26 and fired a torpedo, causing a shock wave that ripped the ship in half.

North Korea, however, denied involvement in the sinking on Thursday and accused the South of fabricating the evidence. It warned that any punishment against the North could trigger war.

“We had already warned the South Korean group of traitors not to make reckless remarks concerning the sinking of warship Cheonan of the puppet navy,” the state-run Korean Central News Agency said Thursday in a characteristically bombastic message regarding South Korea.

The South Korean investigation team did not discuss possible responses to the attack during a press conference held at South Korea’s Ministry of National Defense to announce its findings.

South Korean officials are expected to address responses later and reportedly will ask the United Nations to approve sanctions against North Korea, among other possibilities.

The White House issued a statement Thursday that called the attack “one more instance of North Korea’s unacceptable behavior and defiance of international law.” President Obama said South Korea had the full support of the U.S. during a phone call to South Korean President Lee Myung-bak on Monday.

Fifty South Korean and 15 U.S. analysts were on the Cheonan investigation team, along with nine other analysts from Australia, the United Kingdom and Sweden. Four teams focused individually on scientific investigation, explosive analysis, ship structure management and intelligence evaluation.

According to the team’s findings, two North Korean submarines and an assisting mother ship left North Korean bases two to three days prior to the March 26 sinking and returned to the bases two to three days later. Neighboring countries had no submarines in the area at the time, investigators said.

Lt. Gen. Hwang Won-Dong, an investigation official, said South Korea had not been able to detect the submarine in its waters.

“With the current level of technology anywhere in the world, it is very difficult to detect a submarine,” he said.

According to the investigation team, the recovered torpedo propeller and motor match a North Korean torpedo drawing used in selling the weapons to other countries. The Korean hangul marking of “No. 1” on a piece from inside the torpedo also match markings found in a North Korean torpedo in 2003, according to the team’s report.

Other evidence included explosive powder from the torpedo that was found across the ship, seismic wave activity caused by the explosion, and the upward bending of the ship’s metal hull at points of impact.

Investigators said they also interviewed the 58 survivors of the attack, who said they heard a near-simultaneous explosion once or twice. A sentry on the shore of nearby Baekryong Island saw a 100-meter high flash of white light for two to three seconds, and the recovered bodies of sailors had fractures and cuts but no burns — all typical effects of a shock wave.

Brig. Gen. Yoon Jung-sung, head of the scientific investigation team, said footage from six of the 11 closed-circuit cameras on the Cheonan had been recovered, showing normal activity on the ship until a minute before the explosion, when the footage stops.

Most of the sailors who died were trapped in the ship’s stern, which housed living quarters and the mess hall. Yoon said none of the sailors survived the minutes beyond the initial blast, even though South Korea continued its search for survivors for days in hopes that some had been able to seal themselves off in part of the ship.

North Korea said Thursday it would send its investigators to conduct a probe.

However, Lt. Gen. Park Jung-i, co-chair of the investigation team, said that because the two countries are still under an armistice put in place after the Korean War, the United Nations Command will conduct its own investigation into North Korea’s involvement in the attack and present its findings to both North Korea and South Korea.

U.S. Forces Korea had no immediate comment Thursday on the investigation findings.

U.N. Secretary-General Ban Ki-moon, a former South Korean foreign minister, called the investigation results “deeply troubling,” his spokesman said in a statement, according to The Associated Press.

China, North Korea’s traditional ally, called the sinking “unfortunate.” Vice Foreign Minister Cui Tiankai refused to comment further other than reiterating the need to maintain peace on the Korean peninsula, AP reported.

Japanese Prime Minister Yukio Hatoyama issued a statement Thursday calling North Korea’s action “unforgivable” and said Japan plans to continue close cooperation with South Korea and the U.S. in the matter. Japanese Defense Minister Toshimi Kitazawa ordered his senior officials to re-examine the state of the Japan Self-Defense Forces and to continue gathering intelligence.

Stars and Stripes reporter Hana Kusumoto contributed to this report.rowlanda@pstripes.osd.mil

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