According to the statement posted on a militant website, Ahmed al-Rouissi was killed recently in clashes around the Libyan city of Sirte — a stronghold for the Islamic State group in Libya.
The 166th Battalion, a militia loyal to the Libyan government in Tripoli, is fighting to take Sirte back from the IS group's Libyan affiliate.
Libya's internationally recognized parliament has been forced from the capital and meets in the eastern city of Tobruk. It is currently in talks with its Tripoli-based rival about forming a national unity government.
Al-Rouissi was one of the most wanted men in Tunisia, where he was considered the mastermind of a string of attacks carried out by the radical Islamist Ansar al-Shariah movement, including the assassination of left-wing politicians Chokri Belaid and Mohammed Brahmi.
Their deaths plunged Tunisia into a political crisis that eventually led to the resignation of the elected Islamist government.
Al-Rouissi fled to Libya where he began fighting under the banner of the Islamic State group, which already controls about a third of Syria and Iraq in a self-declared caliphate.
Tunisia's Interior Ministry has not confirmed al-Rouissi's death, though the local press has been filled with reports on the incident.
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