"A mine exploded under their vehicle," ministry spokesman Belhassen Oueslati told AFP, declining to name the exact location where he said a military operation was "ongoing".
"The mine was planted by terrorist elements," he added.
The incident comes as the country is on high alert after gunmen killed 20 foreign tourists and a policeman at the country's national museum on Wednesday, in an attack claimed by the Islamic State group.
Deadly ambushes on the police and army are common in the region, where cross-border smuggling of fuel and food is also rife.