a "blessed invasion of one of the dens of infidels and vice in Muslim Tunisia,"
Nine people have been arrested in connection with a gun attack in Tunis that saw 23 people killed on Wednesday, including 20 foreign tourists.
Tunisia's presidency said four of those arrested were directly linked to the attack and five had "ties to the cell".
The army will also be deployed to major cities, the presidency added.
In another development, Islamic State said it was behind the attack on the Bardo museum, using an audio message to praise two "knights of the caliphate".
The message, posted on Twitter accounts known to be reliable sources of IS propaganda, named the attackers as Abu-Zakariya al-Tunisi and Abu-Anas al-Tunisi.
The recently expanded Bardo Museum features Roman mosaics and is located close to the Tunisian Parliament building. Making this "a new blow to the tourist industry that is vital to Tunisia as it struggles to consolidate the only transition to democracy after the Arab Spring revolts."
Tunisian officials had initially said that the attackers took 10 hostages and killed nine people, including seven foreign visitors and two Tunisians. When security forces retook the museum about four hours later, however, the death toll more than doubled, raising questions about how and at what point the hostages had died.