TUNIS (AFP) - Eight people arrested over a deadly attack on Tunisia's National Bardo Museum have been freed, including a man named at the time as a key suspect, the justice minister said on Thursday.

"Seven people were released yesterday (Wednesday) and another one today," Justice Minister Mohamed Saleh Ben Aissa told AFP.

He said a magistrate had ordered the releases but would not say on what grounds or how many remained in custody over the March 18 attack in Tunis, during which two young Tunisians gunned down 21 foreign tourists and a policeman before being shot dead.

The Islamic State in Iraq and Syria militant group claimed the attack, although authorities pointed to a militant cell headed by Mohamed Emine Guebli who was among those released.

Tunisian authorities have announced a total of 46 arrests over the museum massacre.