Radical militants have killed four members of Tunisia's national guard in the mountainous Kasserine region near the Algerian border.
A statement issued by Tunisia's Interior Ministry says the attackers escaped after taking the guardsmen's weapons.
The attack took place near Mount Chaambi, a national park on the Algerian border that has provided refuge to al Qaida linked Islamist radicals blamed for attacks against the army and politicians in Tunisia over the last two years.
The attack comes as Tunisian forces on the Libyan border are on high alert in the wake of the murder of 21 Egyptian Christians in Libya by another radical Islamic group.
Tunisia is battling radical militants with links to extremists in neighbouring Algeria and Libya.