"There are developments in the case, but to protect the secrecy of the investigation we prefer not to provide any details," prosecution spokesperson Sofiene Sliti told the AFP news agency on Saturday.

Interior Minister Mohamad Ali Aroui was more forthcoming with details, saying "more than 10 people have been arrested for direct or indirect involvement in the attack, among them people who provided logistical support."

Aroui would not be pushed on whether that figure included the nine people already reportedly arrested, including the father, sister and two brothers of one of the gunmen killed by police in Wednesday's attack, Jabeur Khachnaoui.

Two Tunisians, believed to have trained in neighboring Libya where the "Islamic State" (IS) is thought to have training camps, opened fire in the National Bardo Museum on Wednesday. The gunmen targeted tourists, killing 21 people, including a policeman.

Without going into detail, the interior minister also said that an arrest warrant had been issued for a Tunisian national, Maher Ben Mouldi Kaidi, suspected of being involved in the attack.

Four Italians, three Japanese, three French, two Spaniards, a Colombian, and Australian-Colombian, a British woman, a Belgian woman, three Poles and a Russian were killed in Wednesday's attack.

On Thursday, IS claimed it was behind the attack.

Tunisia has seen an increase in Islamist extremism since the 2011 revolution that ousted Zine El Abidine Ben Ali and began the Arab Spring.

jlw/msh (AP, AFP, Reuters)