"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.
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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.
Since its 2011 revolution, Tunisia has seen a rise in Islamist extremism. For the past two years, the army has been hunting Al-Qaeda-linked jihadists who are active in the border area.
Deadly ambushes on the police and army are common in the region, where cross-border smuggling of fuel and food is also rife.