South Korean authorities continue to probe the mysterious sinking of a naval ship last month in the Yellow Sea, but authorities haven't discounted a theory that North Korea could have sunk the vessel.
Seoul has avoided blaming North Korea and North Korea sloughed off allegations it is responsible. Yonhap news agency reports that authorities have yet to find "concrete evidence, such as fragments of a torpedo" to back up evidence of North Korean involvement.
The 1,200-ton patrol ship Cheonan sunk near the western sea border with North Korea on March 26, Thirty-eight of Cheonan's 104 crew members have been confirmed dead, and eight more are also believed dead, though they are still listed as missing. The 58 others were rescued before the vessel sank.
Intelligence authorities immediately assumed North Korea could be to blame, according to a senior military source quoted by Yonhap on Thursday. That assessment was reported to the presidential office and the Defense Ministry right after the incident.
"Since February last year, North Korea has strengthened training that showed the possibility of it launching a guerrilla warfare-style provocation, rather than a skirmish," the source said.
North Korea and South Korea fought gun battles with each other in 1999, 2002 and in November near the location of the incident.
Defense Minister Kim Tae-young told parliament on Monday of South Korea's immediate suspicions over North Korea. He said that reaction prompted a nearby South Korean warship to fire at an unidentified object "speeding northward." The object was later determined to be a flock of birds.
Kim has said that a sea mine or torpedo appear the most likely causes. The media has been rife with speculation - theories range from an internal boiler explosion to a North Korean naval special forces attack.
After the vessel's wreckage was initially examined last week, a South Korean investigator blamed an unidentified "external explosion" as the most likely cause.
"There is a higher possibility of an external rather than an internal explosion," said Yoon Duk-yong, the co-head of a government-appointed team to investigate the incident. Yoon's comment was based on a preliminary investigation of the stern wreckage. But it is necessary "to make a detailed analysis, leaving all possibilities open," he said.
Choi Sung-yong, head of the Abductees Family Union, a South Korean group that helps abductees and prisoners of war escape from North Korea, insists that North Korea sunk the ship.
He said a North Korean mini-submarine with a 13-man crew sank the ship. He cited a trustworthy informant in the North Korean military for his information and his claim was reported in South Korea's bestselling daily newspaper, the Chosun Ilbo, on Tuesday.
But Choi conceded "there is no definite way to confirm the facts."
U.S. and Australian experts are helping South Korea determine the cause of the sinking.
South Korean Defense Ministry spokesman Won Tae-jae has suggested the possibility of deploying more weapons and radar systems to the country's five northernmost islands near the border with North Korea. He also said a plan to cut troop levels on those islands will be scrapped, Yonhap reported. - Journalist Andrew Salmon contributed to this report