North Korea denied it was responsible for the sinking and threatened to retaliate against any attempt to punish it with "all-out war.''
We "will regard the present situation as the phase of a war and handle all problems in inter-Korean relations accordingly,'' Ri Chung Bok, deputy director of the secretariat of the committee for the peaceful reunification of Korea, said in an interview with television broadcaster, APTN, in Pyongyang, the North's capital, on Friday.
The US said it wants South Korea to lead the way in coming up with possible responses to Thursdays' report from the investigation team.
US officials have refused to call the North's attack on the ship an act of war or state-sponsored terror, warning that an over-reaction could cause the Korean peninsula to "explode.''
They said they would explore diplomatic steps through the UN or increase Washington's unilateral sanctions against the North.
Lee Myung-bak, South Korea's president, said during an emergency meeting in Seoul, the South's capital, on Friday that the South would be prudent in responding to North Korea's "military provocation".
|The sinking has sparked protests in South Korea with calls for a tough response [Reuters]
"Since this case is very serious and has a grave importance, we cannot afford to have a slightest mistake and will be very prudent in all response measures we take," Lee was quoted as saying.
South Korea said it has no plans for a retaliatory strike, saying instead it will press for more sanctions against Pyongyang.
It also wants the North to be returned to the US list of state sponsors of terrorism.
South Korea's Cheonan was hit by an explosion, broke in two and sank in the Yellow Sea off the west coast of the Korean peninsula on March 26 while it was on "a routine mission."
The ship was later salvaged from the sea bed and is in dry dock at a naval base south of Seoul.
The investigation team included experts from the US, Britain and Sweden.
The team's report said Korean markings found on salvaged parts from the torpedo matched markings on a stray North Korean torpedo recovered by the South seven years ago.
According to the report the Cheonan was split apart by a shockwave and bubble effect produced by the underwater explosion of a torpedo.
It said torpedo parts recovered including the propellers, propulsion motor and a steering section "perfectly match the schematics of the CHT-02D torpedo shown in brochures provided to foreign countries by North Korea for export purposes".
|Investigators said recovered remains were identical to a North Korean torpedo [AFP]
"The evidence points overwhelmingly to the conclusion that the torpedo was fired by a North Korean submarine," the joint civilian and military investigation team said.
"There is no other plausible explanation."
Pyongyang has condemned the report as a "sheer fabrication", accusing the South's conservative government of using the incident for political gain and to worsen already chilly ties between the two Koreas.
North and South Korea remain technically at war having never signed a formal peace treaty to end the 1950-53 Korean War.
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.
North Korea has said it plans to send its own investigators to the South to look into the causes of the sinking.
But South Korea's Yonhap news agency on Friday quoted a source in the South's defence ministry as saying it had no intention of allowing such a delegation.