"A bubble jet caused by a heavy torpedo [attack] is thought to be one of the most likely things to be blamed, but various other possibilities are also under review," said Defence Minister Kim Tae-Young, the first minister to explicitly talk about an underwater explosion.
The stern of the ship was raised Saturday, and investigations indicate it was hit by the force of a blast.
“After the initial visual inspection of the severed surface and the inside/outside of the hull, we assume the cause is underwater explosion," said Yoon Duk-Yong, co-chairman of a joint international investigation team that included US and Australian experts, in an interim report released Sunday.
"It is highly likely that a non-contact explosion was the cause rather than a contact explosion," he said, without specifying what type of explosive had been used.
Pyongyang has accused Seoul of shifting the blame to the North. Shortly after the vessel sank on 26 March, the Defence Minister said a mine or a torpedo could have been the cause, but since then South Korea has been careful not to blame the North.