Tunisian armed forces say they have launched an offensive against Islamist militants near the Algerian border.
Early-morning shelling was heard in the mountains near Kasserine, 280km (174 miles) south west of Tunis.
On Monday, gunmen suspected of links to al-Qaeda ambushed and killed eight soldiers. Algeria says its forces will help Tunisia find the attackers.
Tunisia's Islamist-led government faced public anger when an opposition figure was assassinated on 25 July.
"A huge operation, with ground and air units, was launched at dawn," an unnamed military spokesman told Tunisia's Mosaique FM radio.
Soldiers clashed on Thursday night with members of "a terrorist group" in the Mount Chaambi district, the radio reported. Tunisian troops and special forces managed to surround the militants, who numbered between 10 and 15, a Tunisian security source told the Reuters news agency.
A military source on the ground told AFP news agency that helicopters had carried out air strikes about 16km (10 miles) from the town of Kasserine. "Either they give themselves up or they will be killed," he said.
The soldiers killed in the ambush on Monday were found near Mount Chaambi. Their throats had been cut.
Media reports in Algeria says its military presence has been boosted near the border, in co-ordination with Tunisian security forces, due to increased tensions in the area.
The moderate Islamist-led government of Tunisian President Moncef Marzouki has faced street protests after the killing of left-wing MP Mohamed Brahmi. He was the second opposition figure to have been killed in the country since February.
Both the opposition and government supporters plan to hold demonstrations this weekend.