By Patrick Markey
TUNIS (Reuters) - Tunisia said on Thursday that an attack on a Tunis museum last week was launched by a cell of 23 militants, including an Algerian and Moroccans, with overlapping allegiances to a number of hardline islamist groups.
Tunisian Interior Minister Najem Gharsalli said 80 percent of the group had already been arrested over the killing of 20 tourists including Japanese, French and Italians in an attack claimed by the Islamic State group.
"This cell is linked to Okba Ibn Nafaa and Al Qaeda in Islamic Maghreb, most of them came originally from Ansar al Sharia," Gharsalli said. "It is a group of 23 people, including two Moroccans and an Algerian, but 80 percent of them are already arrested."
Ansar al Sharia is listed as a terrorist group by Washington. Okba is mainly based in the Chaambi mountains bordering Algeria. That group has been tied to al Qaeda in the Islamic Maghreb's original Algerian leadership. But it has also issued ambiguous statements about the Islamic State..
Lines are blurring between Islamic militants in North Africa as members of local al Qaeda affiliates are drawn to Islamic State's high-profile attacks following its success in seizing swathes of territory in Iraq and Syria last year.
Islamic State split off from al Qaeda and shares its violent Salafist Sunni Muslim ideology. Some militants who once stood with al Qaeda have embraced Islamic State's self-declared "caliphate" in Iraq and Syria to take on its banner.
More than 3,000 Tunisians have left to fight in Iraq and Syria and the government is concerned those who return will carry out more attacks on Tunisian soil.
Islamic State is already gaining a foothold in the chaos of neighboring Libya, where two rival governments battle for control.
The Bardo attack is testing Tunisia just as the North African country is being hailed as an example for democratic transition four years after its "Arab Spring" uprising to oust autocrat Zine El-Abidine Ben Ali.
Western leaders, including France's Francois Hollande and Italy's Prime Minister Matteo Renzi, are expected for a large march in solidarity on Sunday, local officials said.
Since its 2011 revolution, Tunisia mostly avoided the turmoil facing other "Arab Spring" countries. Secular and Islamic politicians have compromised to make their transition work, approve a new constitution and hold free elections.
But security forces have been waging a low-level war against Islamist militants. Until the Bardo attack though most militant assaults were focused on security forces in remote areas.
(Additional reporting by Tarek Amara; editing by Ralph Boulton)