Thirty-eight foreigners, most British holidaymakers, were killed in Friday's attack before the gunman was shot by police. In March, two gunmen killed 21 people at the Tunis Bardo museum, before they were also shot.
"This is a group who were trained in Libya, and who had the same objective. Two attacked the Bardo and one attacked Sousse," Lazhar Akremi, minister for parliamentary relations, told reporters late on Wednesday. "Police are hunting for two more."