The clashes followed the shooting deaths of seven civilians in the northern Jaffna peninsula Thursday after a grenade attack wounded three soldiers in the same area, a pro-rebel website reported.
In the latest action, government forces attacked several rebel Tamil Tiger boats off the island's northwest, destroying one vessel and a truck transporting reinforcements, the military said.
Naval craft confronted at least four boats of the Liberation Tigers of Tamil Eelam (LTTE) near Kuthirimalai Point off the coastal district of Mannar, they said.
Defence ministry spokesman Prasad Samarasinghe said a helicopter gunship destroyed the rebel truck which he said was transporting a heavy gun to the coast to attack the navy.
He had no details of Tiger casualties.
The navy has accused the rebels of gun-running in the area where the island's ethnic conflict simmers.
Friday's air and naval strikes came ahead of Saturday's visit by Tokyo's special peace envoy Yasushi Akashi for talks