The Sri Lankan navy said it killed at least 15 Tiger guerrillas after sinking three craft off the island's northwest coast on Saturday.
Helicopter gunships and supersonic jets also bombed rebel boats, the navy said.
However, the Liberation Tigers of Tamil Eelam (LTTE) said they sank at least two Sri Lankan patrol craft and that 10 sailors died.
The sea battle came as Tiger rebels set off a powerful landmine in the northern district of Vavuniya that killed five soldiers and wounded two more, police officials said.
They also said five students were killed and another eight seriously wounded after a blast near an agricultural school and believed the incident happened when troops opened fire because they suspected the group planned to detonate a mine.
On Sunday, both the Tigers and the security forces accused each other of blocking essential food and medical supplies to the embattled Vakarai in the eastern district of Batticaloa.
"As a result of Tiger disturbances, the (food) co