The air raids came as nine were held over Friday's bus bombing
Tamil Tiger rebels have bombed military targets in the north-east of Sri Lanka using light aircraft.
Two military installations were hit by the rebels across the front line in the Welioya region, a security source said.
They dropped three bombs before flying back, the military said. Security forces have just launched a fresh drive against the Tigers in the area.
It was the fifth rebel aerial strike since the Tigers created an air force a year ago.
The attack came as police arrested nine people over a suspected rebel bomb blast that killed 26 people on a bus near the capital, Colombo, during rush hour on Friday evening.
Sunday's attack is said to have caused no damage but would indicate the rebels have the coordinates of military targets.
"They came and dropped three bombs," said military spokesman Brigadier Udaya Nanayakkara.
"Nobody was hurt, and no damage to any property."
Troops on the ground had fired, and Air Force interceptor jets were scrambled, but the planes got away, he added.
The rebels have a number of Czech-built, two-seater, propeller-driven aircraft which were reportedly smuggled into the country in pieces before being reassembled and modified to carry bombs, says the BBC's Roland Buerk in Colombo.
This was the first time the planes have been deployed since last October, when they backed up a ground assault on an air force base in Anuradhapura by a Tiger suicide squad, our correspondent adds.
The Tigers have fought for a generation for an independent state for the Tamil minority.
At least 70,000 people have died since the civil war began in 1983.