A group of Tamil Tigers tried to sneak across the front lines into the northern Jaffna Peninsula on Thursday, sparking a gun battle with troops that killed three of the rebels, said Brigadier Udaya Nanayakkara, a military spokesman.
Two more rebels were killed in separate confrontations in the Mannar and Vavuniya districts south of rebel territory, he said.
In another incident near Vavuniya on Thursday afternoon, a soldier was killed in a gun battle with Tamil Tiger fighters.
The Tamil Tigers have been fighting since 1983 to create an independent homeland for minority Tamils in the northeast.
More than 70,000 people have been killed in the conflict.