Islamist militants disguised as security officials killed three Tunisian policemen and a civilian in an attack near the border with Algeria, the state news agency TAP said on Sunday.
The agency did not name any group in the attack. Tunisia's security forces have been battling militants from the banned Islamist movement Ansar al-Sharia, whose leader has declared allegiance to al Qaeda's North Africa wing.
TAP said four gunmen dressed as Tunisian security officials killed the four and wounded two police and a border agent just after midnight in d'Awled Manna, in northwest Jendouba province.
The militants stole weapons and a vehicle, TAP said.
Ansar al-Sharia was one of the most hardline Islamist groups to emerge after Tunisia's 2011 uprising against autocrat Zine el-Abidine Ben Ali, whose government often jailed Islamist leaders.
One of the Arab world's most secular countries, Tunisia has progressed in its transition to democracy after the revolt, with a new constitution praised for its modernity and elections scheduled for this year.
But Islamist militant violence is one of the main challenges for the new caretaker government. Earlier this month, police killed seven militants armed with suicide bomb vests and explosives in a raid north of the capital.
Ansar al-Sharia led by a veteran of Afghanistan's conflicts, was blamed for storming the U.S. embassy in Tunis in 2012 and is listed by Washington as a foreign terrorist organisation, with ties to al Qaeda in the Islamic Maghreb.