20-year-old Tunisian shepherd beheaded in 'probable terror attack'
"The decapitated body of a young man has been found... and it is probable that a terrorist group was behind the attack," senior prosecutor Mohsen Dali said, naming the victim as 20-year-old Oqba al-Dhibi.
An investigation was underway, he added.
Local radio said Dhibi was a shepherd who was tending his flock when he came under attack.
There was no immediate claim of responsibility.
Attacks have been carried out in the same mountainous areas of central Tunisia before, some 225 kilometres (140 miles) south-west of the capital.
In 2015, teenager Mabrouk Soltani was beheaded by an extremist group, a killing that shook public opinion.
Two years later, his older brother, Khalifa Soltani, was found dead after he was reported kidnapped by a gang in the same region.
Those two killings were claimed by the Islamic State group (IS).
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The mountainous central region of Tunisia is also a hideout for the Tunisian branch of jihadist group Al-Qaeda in the Islamic Maghreb (AQIM), known as Okba Ibn Nafaa.
Tunisian Prime Minister Hichem Mechichi, in a brief statement, denounced a "terrorist operation", stressing that the struggle "must continue unabated."
Since its 2011 revolution, Tunisia has been hit by a string of jihadist attacks that have killed dozens of security personnel, civilians and foreign tourists.
While the situation has significantly improved, Tunisia has maintained a state of emergency.
Agencies contributed to this report.