The latest finding is expected to further back suspicions that a torpedo attack caused the explosion of the 1,200-ton patrol ship Cheonan near the tense Yellow Sea border with North Korea on March 26. The Cheonan broke in two and sank, killing 46 sailors.
"Explosive traces found in the Cheonan's chimney and the seabed on which the stern's broken-off side had been lying were all confirmed as those of the high explosive RDX, which is more powerful than TNT," the official said on condition of anonymity. "This explosive is used in torpedoes, not sea mines."
RDX, which stands for research department explosive, is a white crystalline solid and is considered the most powerful high explosive and a main ingredient in plastic explosives.
Four alloy fragments have also been found in the wreckage, which was salvaged last month, and an analysis has showed that they were an alloy of aluminum and magnesium used in a torpedo's casing, the official said.
Investigators are also looking into the possibility that a German-made torpedo might have been used in a move by North Korea to disguise the attack, as South Korea and the United States use German torpedoes.
Foreign specialists from the United States, Sweden, Australia and Britain have joined South Korea's investigation into the sinking, as Seoul sought to ensure the probe is transparent and objective.
After the investigation is complete, South Korea could invite experts from China and Russia, countries close to North Korea, to provide them with a first-hand look at the ship's wreckage, Defense Ministry spokesman Won Tae-jae said.
Won said the outcome is expected to come before the end of this month.
Earlier this week, President Lee Myung-bak told a conference of top military generals that the sinking was not a "simple accident," while Defense Minister Kim Tae-young said a "surprise attack" sank the vessel, although neither directly mentioned the communist neighbor.
North Korea has denied any responsibility.
Suspicions of North Korea's involvement have been strong, as the site of the sinking lies near where the navies of the two Koreas fought deadly skirmishes in 1999, 2002 and most recently in November last year.
source: Yonhap News