Three Tunisian soldiers were killed on Wednesday when suspected militants opened fire on a minibus carrying troops and their families, the defence ministry said.
"Three soldiers succumbed to their wounds and 12 others were injured, two seriously," spokesman Belhassen Oueslati said after the incident in northwest Tunisia.
The attack occurred in the region of Nebeur, between the towns of Kef and Jendouba, close to the border with Algeria, he said.
"This was a terrorist operation," he added, without providing details on the identity of the alleged attackers.
Since its 2011 uprising Tunisia has witnessed frequent attacks by jihadists that authorities say have killed dozens of police and military personnel.
Security forces have engaged in a crackdown on militant groups close to the border with Algeria since the end of 2012.
The authorities have voiced fears that extremists might try to disrupt landmark elections.
The country is preparing for presidential polls on November 23 -- the first time Tunisians freely elect their head of state -- following a key parliamentary election last month.