Tuesday's fighting came a day after two bombings blamed on suspected rebels killed at least 15 people.
On Monday, a roadside bomb attack on a civilian bus in the Welioya region about 240km northeast of Colombo, killed 14 people and wounded 15 others, marring celebrations of the country's 60th independence day.
Another roadside bombing in the southeastern town of Buttala killed one soldier and injured two others, the military said.
Sri Lanka staged mass funerals for the bomb blast victims on Tuesday.
The government has delayed by three days a military hardware and state enterprise exhibition after the blasts.