Tunisia's Defense Ministry says gunmen have attacked a bus carrying soldiers and their families in the mountainous northwest region, killing three service members and wounding 12 people.

Ministry spokesman Rachid Bouhoula said the attack took place Wednesday near El-Kef, part of the rugged border region with Algeria. It wasn't immediately known if the wounded included civilians.

In Tunisia many soldiers live with families on bases with their own transportation networks between towns.

Al-Qaida-linked extremist groups are believed to be hiding out in these border regions and have mounted several attacks against soldiers.

Tunisia is in the midst of the campaign for presidential elections to be held Nov. 23.

The past year has seen a major crackdown against extremist groups, including occasional standoffs between security forces and militants.