A South Korean navy warship that sank near a tense maritime border with the Democratic People's Republic of Korea (DPRK) in March was torpedoed by a DPRK submarine, a multinational team of investigators announced Thursday.

The group of civilian and military experts said the 1,200-ton warship Cheonan went sunk as a result of an "external underwater explosion" caused by a torpedo fired by a DPRK submarine, resulting in one of the worst peacetime casualties in the country's naval history.

"The evidence points overwhelmingly to the conclusion that the torpedo was fired by a North Korean (DPRK) submarine. There is no other plausible explanation," they said in a statement.

The torpedo was manufactured by the DPRK, it said.

The statement said the joint civilian-military investigation group (JIG) assessed that "a strong underwater explosion generated by the detonation of a homing torpedo below and to the left of the gas turbine room" caused Cheonan to split apart and sink.

The statement said, the propulsion parts, including propulsion motor with propellers and a steering section that have been collected from the site of the sinking, matched in size and shape with the specifications on the drawing presented in introductory materials provided to foreign countries by the DPRK for export purposes.

The marking in Hangul (Korean words), which reads "1 ben," or No.1 in English, found inside the end of the propulsion section, is consistent with the marking of a previously obtained the DPRK torpedo, it said, adding that this evidence allowed the JIG to confirm that the recovered parts were made in the DPRK.

President Lee Myung-bak has vowed to take "firm measure" against the DPRK over the sinking of its warship.

The DPRK has denied its involvement in the accident in April.

On Wednesday, DPRK's Committee for the Peaceful Reunification of Korea released a statement accusing South Korea of taking advantage of the sinking of its warship to push north-south relations to a catastrophe.

In the statement, the committee said the campaign against the DPRK launched by South Korea after the accident reached the height of its confrontation and war moves.