Lt Col Belhassen Oueslati, a Defense Ministry spokesman, said the incident occurred yesterday in a mountainous region near the Algerian border.
Al-Qaeda linked radicals have staged attacks against army and politicians in the area for the past two years.
The incident comes days after the Islamic State group claimed responsibility for an attack that killed 21 people at a museum in Tunis. Authorities say the two slain gunmen blamed for that attack had no clear links to extremists.