Seoul, South Korea (CNN) -- An explosion at close range, and not a direct hit, caused the 1,200-ton patrol ship Cheonan to sink last month, a team of South Korean military and civilian investigators has tentatively concluded.
The investigators' determination was reported Sunday by the Yonhap news agency.
"Instead of being directly hit by a torpedo or other underwater weapon, the Cheonan was affected by a strong explosion that occurred below its bottom at a close range," the news agency quoted a government official as saying.
The explanation matches one that investigators offered shortly after the ship's stern was salvaged 10 days ago.
A final result is not expected for a month, Defense Minister Kim Tae-young told reporters.
He said that the most likely cause of the sinking was a "bubble jet" created by the external explosion under the ship.
A bubble jet effect occurs when an explosion goes off under a ship. The change in pressure causes a huge column of water that strikes the ship with great impact.
On Saturday, recovery crews found the body of a missing sailor in the wreckage of the ship.
The ship sunk in the Yellow Sea near the western sea border with North Korea on March 26.
Forty of Cheonan's 104 crew members have now been confirmed dead, and six more are also believed dead, though they are still listed as missing.
Fifty eight others were rescued before the vessel sank.
South Korea has not ruled out a theory that North Korea was involved.
But Seoul has avoided directly blaming North Korea, which sloughed off allegations it is responsible.
The families of the dead sailors began a five-day mourning period on Sunday.
On Thursday, the South Korean navy will hold a funeral ceremony at a naval command in Pyeongtaek, about 70 kilometers (43 miles) south of Seoul.
The navy has also decided to posthumously promote the dead seamen by one rank and award them a military honor for their patriotism.