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.

A statement described the attack as a "blessed invasion of one of the dens of infidels and vice in Muslim Tunisia".

One of two gunmen involved in the Bardo museum attack, named by Tunisian officials as Yassine Laabidi, was reportedly known to the authorities.

Tunisian Prime Minister Habib Essid told RTL Radio that security services had flagged him up but were not aware of "anything specific", or of any links to known militant groups.

Laabidi and his accomplice, named as Hatem Khachnaoui, were killed as security forces stormed the museum.

It was not immediately clear how the identities of the gunmen corresponded to the names given by IS. Jihadist groups, including IS, often give their fighters noms de guerre.

Tourists from Japan, Colombia, Australia, the UK, and several other European countries were killed in the attack and more than 40 people were injured.