Tunisian Prime Minister Habib Essid has named two gunmen behind the attack on a museum in the capital that left 19 people dead as Yassine Abidi and Hatem Khachnaoui.
The assailants are "probably" Tunisian, according to the interior ministry spokesman.
The authorities gave no further details about the attackers but said there could be two or three accomplices still at large.
17 foreign tourists were among those killed on Wednesday when gunmen dressed in military uniforms opened fire at visitors as they got off a bus and then chased them inside the National Bardo Museum.
No group has claimed the attack, which lasted about four hours and also left two Tunisians dead and more than 40 people wounded.
Tunisia has seen an upsurge in Islamist extremism since the 2011 revolution that ousted longtime strongman Zine El Abidine Ben Ali and sparked the Arab Spring uprisings around the region.
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