Okba Ibn Nafaa, whose militants Tunisian armed forces have been hunting in mountains near the Algerian border for two years, has identified itself with Al-Qaeda in the Islamic Maghreb, the international jihadist network's North African branch.
On Tuesday, AQIM and the Yemen-based Al-Qaeda in the Arabian Peninsula (AQAP) urged jihadists in Iraq and Syria to unite against the common threat from a US-led coalition assembled to fight IS.
"They are urging it to move forward in breaking the borders and crushing the thrones of the tyrants everywhere," SITE quoted a statement on Facebook as saying.
The Tunisian army accused the jihadists in July of killing 15 soldiers in the restive border region in the bloodiest day in the army's history.
Several weeks before that, the group claimed an attack on the home of the interior minister.