“The president has decided large cities will be secured by the army,” his office said in a statement.
Witnesses said the attack came without warning, as two buses bringing Italian tourists to the museum stopped near the main entrance.
The two gunmen, named by the authorities as Tunisians Abidi and Hatem Khachnaoui, had been waiting in the forecourt. They opened fire on the buses, then sprinted for the glass doors of the museum.
Ali Eddine Hamadi, the 22-year-old curator of the Christian relics department, told how he hid tourists from the killers.