Eight Tunisian soldiers have been killed by gunmen near the Algerian border, the president's office said, in what appeared to be one of the biggest attacks on the country's security forces in decades.
The incident on Monday occurred in the remote area of Mount Chaambi, where Tunisian troops have been trying to track down armed groups since December last year.
Adnan Mancer, Tunisia's presidential spokesman, told the Associated Press news agency that the attack took place on Jebel Chaambi, Tunisia's tallest mountain and a suspected hideout of al-Qaeda-linked armed groups.
The army has been searching the mountainous region near the Algerian frontier since a patrol was hit by a roadside bomb in April.
On June 24, the army declared the mountain cleared of "extremists" in a campaign that cost three lives and left 27 soldiers injured.
In the course of its operation, the army discovered evidence suggesting an al-Qaeda-linked movement supported by the local population had set up training camps in the area.
Late on Monday, Moncef Marzouki, the Tunisian president, announced three days of national mourning for the soldiers.