Three soldiers were killed when Tamil Tiger rebels detonated a bomb in the northern district of Vavuniya on Tuesday, the ministry said, adding that another soldier was killed in a similar blast in the Jaffna peninsula.
Four Tamil Tiger rebels were killed in a firefight in eastern Sri Lanka, the defence ministry said, as sporadic artillery duels raged elsewhere.
A security force patrol confronted the four rebels at a village in Batticaloa district Monday and the guerrillas died in an exchange of fire, the ministry said.
"The security forces suffered no casualties during the incident," the ministry added.
It said the guerrillas had also fired artillery at military positions along a de facto front line in the northern peninsula of Jaffna during the night and the security forces retaliated in kind.
There were no immediate reports of casualties on either side.

Copyright AFP (Agence France-Presse), 2006