Tunisia has arrested a cell of 17 Islamist militants and prevented a major assault on hotels and security forces in the resort town of Sousse planned for this month, a senior government official told Reuters on Tuesday.

Sousse was the site of one of two major attacks claimed by Islamic State in Tunisia this year, when 38 foreigners were killed at a beach hotel in June. In March, gunmen killed 21 tourists in an attack at the Bardo Museum in Tunis.

"We have foiled a major attack this month that the terrorist cell was preparing against vital installations, hotels, security centres and against politicians to bring chaos to the country," Interior Ministry security chief Rafik Chelli said.

Chelli said some of the militants had been trained in Libya and Syria and were awaiting orders to carry out the assault.

He said Kalashnikov rifles, explosives and a bomb belt were also seized during the arrests.

Four years after an uprising ousted autocrat Zine El-Abidine Ben Ali, Tunisia has been hailed as an example of democratic transition for the region. One of the Arab world's most secular nations, Tunisia now has a freely-elected coalition government, and a new constitution.

But more than 3,000 Tunisians have travelled to fight for Islamist militant groups in Syria, Iraq and neighbouring Libya. Some of those jihadists have threatened to return home and carry out attacks on Tunisian soil.

The three gunmen involved in the attacks in Tunis and Sousse this year had also trained in jihadi camps across the border in Libya, according to Tunisian authorities, who have started building a wall along the frontier with Libya.

Last week, Islamist militants beheaded a teenager in the central province of Sidi Bouzid and sent his head to his family after accusing him of spying for the military.

Tunisia's army is fighting a low-level conflict against a group of militants holed up in the Chaambi mountains bordering Algeria. Militants occasionally attack security forces from their mountain base.  - Reuters