Militants killed nine Tunisian soldiers and stripped them of their weapons Monday near the Algerian border, as thousands demonstrated against the Islamist-led government.
The soldiers were found with their throats cut, and had been stripped of their weapons and uniforms after an armed group ambushed them, said medical and military sources in Kasserine near Mount Chaambi, the site of the attacks.
Four other soldiers were wounded, the sources added, in the area where the army has been tracking Al-Qaeda-linked militants.
State broadcaster Wataniya 1 said that those killed were "members of an elite unit," without giving further details on the clashes.
Residents said that thousands took to the streets in the town of al-Qasreen, near the site of the attack on the army, and many protesters were demanding the government's ouster.
In the capital, Tunis, more than 10,000 took to the streets as well in one of the biggest protests since the opposition began mobilizing against the government.
"Tunisia is free, out with terrorism, out with Ghannouchi," protesters shouted, referring to Rached Ghannouchi, leader of the al-Nahda party.
"Since they (al-Nahda) came all we've seen is a string of catastrophes," said protester Noura Saleh, who was waving a red Tunisian flag and crying. "Get out, we hate you!"
Security forces have been hunting militant Islamists in the rugged Mount Chaambi area near the border with Algeria since December, when a border post was attacked, killing a member of the national guard.
The army intensified its search at the end of April, after landmines planted by the Islamists to protect their base in the border region wounded 16 members of the security forces.
Improvised explosive devices have wounded and killed several other members of the security forces since authorities intensified their hunt for the group in April.
Authorities have said the jihadist group is made up of several dozen Qaeda-linked militants, some of whom fought in the conflict in Mali.
The death of the soldiers comes as Tunisia's Islamist-dominated government faces protests following the killing of an opposition politician on Thursday.
It was the second political assassination since February.
Opposition groups have demanded the resignation of the government and staged nightly protests, particularly in Tunis. But Prime Minister Ali Larayedh firmly rejected these demands on Monday, calling a general election for December 17.