TUNIS (AFP) - Tunisian militants have beheaded a 16-year-old boy after accosting him and his cousin, both shepherds, on a mountainside in the central province of Sidi Bouzid, authorities said on Friday.

Walid al-Waqini of the interior ministry said the mayor of Sawar Soultaniya in the province reported the murder.

"A terrorist group intercepted two shepherds on Mount Meghila and cut off the head of one and handed it to the other to return to his family," Waqini quoted the mayor as saying.

A security source told AFP the pair had been working when "three terrorists headed them off, one raised his gun and fired in the air, the second slaughtered the shepherd with a knife and the third filmed the attack."

There was no known motive for the killing, which was confirmed to AFP by a senior provincial official in Sidi Bouzid.

Tunisia has faced an upsurge in militant violence since its 2011 revolution, but security forces are generally the target.

Several dozen soldiers and police have lost their lives in attacks, most of which are claimed by Al-Qaeda's North African branch.

The Islamic State in Iraq and Syria (ISIS) group claimed an attack that killed 38 foreign tourists at a seaside resort near Sousse in June, and another that killed 21 foreigners and a policeman in Tunis in March.