The North has denied that it was responsible for the explosion and on Friday it cited speculation over its role as a reason for seizing South Korean-owned propertyin a joint-owned resort.
However, the South has not directly blamed the on the North.
Kim Tae-Young, the South Korean defence minister, said a mine or torpedo may have sunk the corvette, but his ministry said it would keep an open mind until the investigation is completed.
One of seven crewmen still missing following the sinking was found when the front section was drained, local media reported. Fifty-eight sailors rescued alive when the vessel sank.
The wreck was then taken by barge to a navy base south of Seoul, the capital, for an investigation by experts from South Korea, the US and Australia.
The rear of the Cheonan was salvaged earlier this week and taken to the same navy base.
South Korea has given no date for the publication of its findings from both parts of the ship.
The ship was on a routine patrol near the disputed sea border between the two countries when the explosion took place on March 26.
The two nations are still technically at as not formal peace treaty was ever signed to end the Korean War of 1950-53.