The rebel Liberation Tigers of Tamil Eelam (LTTE) set off one mine in the Jaffna peninsula, killing a soldier and wounding six others, the ministry said in a statement.
It said five sailors were wounded in a second mine attack in the northeastern port district of Trincomalee while another serviceman was wounded in a third mine attack in the northwestern Mannar district.
Suspected Tiger rebels also shot dead a civilian in the eastern Ampara district, the ministry said.
The latest attacks came as Sri Lanka pressed for the release of a soldier captured by Tamil Tiger rebels following a fierce mortar duel at the weekend that killed at least 16 combatants.
Defence officials said the government hoped that the Tigers would reciprocate President Mahinda Rajapakse's gesture last week of granting security and medical treatment to an ailing rebel spokesman and free the captive.
Despite a February 2002 truce, clashes have escalated between the two sides with more than 850 people kill