It said torpedo parts recovered including the propellers, propulsion motor and a steering section "perfectly match the schematics of the CHT-02D torpedo included in introductory brochures provided to foreign countries by North Korea for export purposes".
"The evidence points overwhelmingly to the conclusion that the torpedo was fired by a North Korean submarine," the joint civilian and military investigation team, that also included experts from the United States, Britain and Sweden, said in the report on the March 26 sinking.
|Etchings on salvaged parts matched those on a North Korean torpedo recovered earlier [AFP]
"There is no other plausible explanation."
Intelligence gathered with the South's allies - the US, Britain and Australia - showed North Korean submarines were likely in operation near the scene of the sinking, with similar vessels of other neighbouring countries all inside their territorial waters.
"Based on all such relevant facts and classified analysis, we have reached the clear conclusion that [South Korea's] Cheonan was sunk as a result of an external underwater explosion caused by a torpedo made in North Korea," the report said.
Following Thursday's announcement, Lee Myung-bak, the South Korean president, promised "resolute countermeasures" to the attack, which sparked national mourning.
But the president gave no immediate details of the countermeasures.
The White House, calling the report "objective and scientific", strongly condemned the deadly attack.
Al Jazeera's Steve Chao, reporting from Seoul, said the report has major implications in terms of North-South relations, as well as the region.
"The South Korean president is expected to approach the UN Security Council to call for tighter sanctions against the North, a call that is already seeing support from Seoul's allies," our correspondent said.
"Our army and people will promptly react to any 'punishment' and 'retaliation' and to any 'sanctions' infringing upon our state interests with various forms of tough measures including an all-out war"
North Korean National Defence Commission statement
"In recent days the South Korean government has been presenting this evidence to a number of countries to gather support … We've already heard support from strong allies such as Australia, the US and Japan."
The North Korean National Defence Commission, in a statement on the official news agency, said it will send its own investigators to the South to check the purported evidence.
"Our army and people will promptly react to any 'punishment' and 'retaliation' and to any 'sanctions' infringing upon our state interests with various forms of tough measures including an all-out war," it said.
The commission, the North's top decision-making body, repeated denials of involvement and threatened "all-out war" in response to any punitive measures such as sanctions.
It accused the South's conservative government of using the incident for political gain and to worsen already chilly ties between the two Koreas, which have yet to sign a formal peace treaty to end their 1950-53 war.
The North refuses to accept the borderline drawn in the Yellow Sea, where the Cheonan went down.
The area was the scene of deadly clashes in 1999 and 2002 and of a firefight last November that left a North Korean boat in flames.