Sri Lankan navy craft sank a suspected Tamil Tiger suicide boat off the island's north-eastern coast on Friday, a military official said.
The navy detected the explosives-laden Liberation Tigers of Tamil Eelam (LTTE) boat off the coast of Mullaittivu district, a military official said.
It exploded in a fireball, the official said, adding that "there were at least two people aboard when it was attacked."
The guerrillas still have a 30-kilometre (18-mile) stretch of coastline in the district where government forces are leading what the defence ministry says is the final phase of their offensive.
On Thursday, troops said they found a submarine-type craft and three other boats that could have been used in suicide attacks during searches in the district of Mullaittivu.
Security forces are trying to capture the last remaining jungle areas controlled by the Tigers in the district where the guerrillas have their main military bases.