Zarzis / AFP
Tunisian forces killed 21 extremists who attacked police and army posts near the Libyan border on Monday in a new spillover of violence that also saw four civilians killed.
It was the second deadly clash in the border area in less than a week.
The defence ministry said that a soldier was also killed in the fighting for an army barracks in the town of Ben Guerdane.
Hospital official Abdelkrim Chafroud said that a 12-year-old was among the dead civilians. He said two security agents were also killed.
Six militants were wounded and detained, defence ministry spokesman Rachid Bouhoula said.
The interior ministry said the militants also attacked a police station and a National Guard post in the town, but those attacks too were repulsed.
Army units were deployed across the town and authorities ordered a nighttime curfew.
They also closed the Ras Jedir border crossing with Libya, as well as the main road connecting Ben Guerdane with the rest of Tunisia through the town of Zarzis, 70 kilometres to the north.
Witnesses said troops were using loudhailers to urge residents to stay indoors. The defence ministry appealed for information on any suspect activity.
The office of Prime Minister Habib Essid said he would hold an emergency meeting with the defence and interior ministers.
Last Wednesday, troops killed five militants in a firefight outside Ben Guerdane in which a civilian was also killed and a commander wounded.
Troops have been on alert in the border area following reports that militants had been slipping across since a US air strike on an IS group training camp in Libya on February 18 killed dozens of Tunisian militants.
At least four of the five militants killed in last week’s firefight were Tunisians who had entered from Libya in a bid to carry out attacks in their homeland, the interior ministry said.
Deadly attacks by IS on foreign holidaymakers last year, which dealt a devastating blow to Tunisia’s tourism industry, are believed to have been planned from Libya.
Tunisia has built a 200-kilometre (125-mile) barrier that stretches about half the length of its border with Libya in an attempt to stop militants infiltrating.
Last month’s US strike on the IS training camp outside the Libyan city of Sabratha targeted the suspected mastermind of two of last year’s attacks, Noureddine Chouchane.
Washington has said Chouchane was likely among the dozens of militants killed, and that the strike probably averted a mass shooting or similar attack in Tunisia.
Chaos has engulfed Libya since the NATO-backed ouster of dictator Moamer Kadhafi in 2011.