The family of one of the gunmen behind the Bardo Museum attacks in Tunis that killed 21 have been arrested.

The father, two brothers and sister of one of the two attackers identified on Wednesday as Hatem Khachnaoui (real name Jabeur Khachnaoui) are in detention, the AFP reported, citing police sources.

The assailant, who was killed and identified on the day of the attack, comes from Ibrahim Zahar, a village in Tunisia's West Central province.

According to these sources, Lobna his sister, his brothers Maher and Mourad and their father were arrested on the night of Wednesday to Thursday by police in the district of Sbiba in neighboring Kasserine region of Algeria, where pious family has a small farm.

The government said Thursday that nine people had been arrested in connection with the investigation into the attack against the Bardo Museum, which killed 21 people including 20 foreign tourists.

The attack was claimed by the Islamic State group.