Tunisian forces killed 28 jihadists who stormed through the Tunisian town of Ben Guerdan near the Libyan border on Monday attacking police and army posts in a burst of violence that killed at least 50 people, including civilians, the government and residents said.

Local television showed images of soldiers and police crouched in doorways and on rooftops as gunshots boomed in the center of the town. Bodies of dead militants lay in the streets near the military barracks after the army regained control.

It was the second deadly clash in the border area in less than a week as Tunisia struggles to avert the large number of its nationals who have joined ISIS jihadist group in Libya from returning to spread terror at home.

Authorities sealed off the nearby beach resort town of Djerba, a popular destination for foreign and local tourists, and ordered a nighttime curfew on Ben Guerdan and closed two border crossings with Libya after the attack. Troops deployed across the border town of Ben Guerdane to chase after others involved in the coordinated pre-dawn attack.

“I saw a lot of militants at dawn, they were running with their Kalashnikovs,” Hussein, a resident, told Reuters by telephone. “They said they were Islamic State and they came to target the army and the police.”

It was not clear if the attackers crossed over the border, but it was the type of militant operation Tunisia’s government had feared as it prepares for potential spillover from Libya, where ISIS militants have taken control.

More than 3,000 Tunisians have left to fight with ISIS and other groups in Syria and Iraq. Tunisian security officials say increasingly they are returning to join the militant group in Libya.

Since its 2011 revolt to oust ruler Zine El-Abidine Ben Ali, Tunisia has battled with jihadists at home and over the border. Militants trained in jihadist camps in Libya carried out two attacks last year in Tunisia.

“This was an unprecedented, well-organized attack,” President Beji Caid Essebsi told local radio. “But the people in the south can be confident the army and police will win against this barbarity across the border.”

The Interior Ministry stated that soldiers killed 33 militants and arrested six. Hospital and security sources said at least seven civilians were killed along with ten soldiers.

Hospital official Abdelkrim Chafroud said a 12-year-old was among the dead civilians.

“If the army had not been ready, the terrorists would have been able to raise their flag over Ben Guerdan and gotten a symbolic victory,” said Abd Elhamid Jelassi, vice president of the Islamist party Ennahda, part of the government coalition.

Since the fall of Muammar Gaddafi five years ago, Libya has slipped into chaos, with two rival governments and armed factions fighting to dominate. ISIS has grown amidst the chaos, taking over Sirte city and drawing foreign recruits.

Tunisian jihadists are taking a lead role in ISIS camps in Libya, Tunisian security sources say.

Tunisian forces have been on alert for possible militant infiltrations since last month when a U.S. air strike targeted mostly Tunisian ISIS militants at a camp near the border in Libya’s Sabratha.

Western military advisers are starting to train Tunisian border forces to help better protect the frontier with electronic surveillance and drones and authorities have built a trench and barrier to help stop militants crossing.