In a BBC interview, South Korean Foreign Minister Yu Myung-hwan speculated that the sinking of the Cheonan might have been the result of internal Pyongyang politics.
North Korea has angrily denied any responsibility for the attack.
The North Korean military, Mr Yu said, might have decided to do it in order to distract attention from other problems.
Mr Yu had no criticisms to make of China for failing to condemn North Korea publicly for the sinking of the Cheonan.
On the contrary, he felt that China had been privately helpful and understanding during the three-way summit with South Korea and Japan, which ended on Sunday.