The following editorial first appeared in The Yomiuri Shimbun:
A multinational investigation has determined that the sinking on March 26 of a South Korean naval warship in the Yellow Sea was caused by a North Korean torpedo.
On Thursday, South Korea's Joint Civilian-Military Investigation Group released the results of its investigation into the incident, concluding that an underwater blast caused by a North Korean homing torpedo tore the Cheonan patrol vessel in two in waters west of the Korean Peninsula.
In a swift reaction to the release of the report, Pyongyang called the results "a fabrication," warning that any retaliation would prompt it to "respond with various forceful actions, including all-out war."
If circumstances take a turn for the worse, North Korea might resort to further flagrant provocations. Japan, the United States and South Korea must work together closely to prevent the reclusive state from behaving recklessly. China and Russia should also act in concert with the three nations.
The team of investigators included specialists from the United States, Britain, Australia and Sweden.
Fragments recovered from the waters where the Cheonan went down - components of a torpedo propulsion device, including a propeller - provided all the evidence needed to determine what happened. The fragments in question matched the schematics of a torpedo included in introductory brochures provided to foreign countries by North Korea for export purposes.
The investigative team's conclusion, supported by these pieces of material evidence, is convincing.
North Korea continues to deny its involvement in the sinking. It should be remembered, however, that Pyongyang has lied about various criminal actions it has been accused of in the past. These include a spate of kidnappings targeting Japanese and a terrorist bomb explosion that occurred in Yangon 27 years ago, killing a number of people, including four South Korean cabinet ministers. Given this, North Korea's denial of its involvement in the sinking of the warship cannot be taken at face value.
The sinking of the Cheonan occurred in waters where repeated clashes between warships from the South and North have occurred. In November, a North Korean warship was damaged in an exchange of fire between South and North Korean ships in the Yellow Sea. Some South Koreans view the torpedo attack as retaliation by North Korea for this exchange of fire.
South Korea is fundamentally reviewing its defense policy in response to the sinking and is expected to further bolster its alliance with the United States. This apparently shows that the South Korean government learned a bitter lesson when it dropped its guard against North Korea as a result of the sunshine policy of engagement with Pyongyang adopted by the preceding left-leaning administration.
The South Korean government is expected to take the issue of the Cheonan's sinking to the U.N. Security Council.
In separate telephone conversations with South Korean President Lee Myung Bak, Prime Minister Yukio Hatoyama and U.S. President Barack Obama pledged to support South Korea in addressing the issue at the Security Council. Japan and the United States should strive to ensure the council adopts a document that raises harsh questions about North Korea's responsibility for the sinking of the Cheonan.
Attention will be focused on whether China will choose to condemn North Korea in response to the release of the latest report. We hope the Chinese government will take a firm stance against North Korea.
Participants in the six-party talks aimed at having North Korea dismantle its nuclear weapons will probably have to postpone a resumption of their negotiations for some time to come. However, doing so will help Pyongyang gain time to further advance its nuclear weapons development program, as it has been unwilling to return to the negotiating table.
North Korea's nuclear weapons program - a direct threat to our national security - must not be left unchecked. With this in mind, Japan needs to look for ways to open a new round of six-nation talks at an early date.