Seven people are being interrogated in Tunisia's capital in the investigation into a deadly beach resort attack that killed 38 people, according to a person with knowledge of the investigation.

The person close to the investigation said that four people were arrested today - two in the resort town of Sousse where the attack occurred, one in the capital Tunis, and one in the restive city of Kasserine. Three others were arrested Sunday.

The person spoke on condition of anonymity because he wasn't authorized to be publicly named.

Earlier, Interior Minister Mohamed Najem Gharsalli said that multiple arrests have been made, but provided no details.

The 24-year-old attacker, who used a Kalashnikov assault rifle and grenades, was killed by police after Friday's carnage in Sousse.