The nine fatalities comprised four men and five women, Gentiloni told the press, adding that relatives had been notified.
A tenth Italian was in the restaurant when the attack unfolded but was not among the 20 listed as dead, he said.
Local media said the Italian dead included a 33-year-woman who had been in Bangladesh for 18 months for work, a 52-year-old woman textile exective and a 47-year-old entrepreneur who was the father of three-year-old twins.
Prime Minister Matteo Renzi had earlier prepared the nation for bad news, saying the country was "like a family which has suffered a painful loss."
The attackers who believed they were "destroying our values" would not get a drop of encouragement from Italy, he said.
"We are stronger," Renzi said.
"The terrorists want to rip away the daily fabric of our lives. Our duty is to reply with even greater force, by affirming our values, the values of freedom of which we are proud, and which are stronger than hatred or terror."
The attackers, moving at the start of the Eid holiday, took foreigners hostage at a restaurant, killing 20 before troops moved in Saturday. Many of the victims were hacked to death.
The Bangladesh military said most of the fatalities were either Italian or Japanese. Thirteen hostages were rescued.
Pope Francis sent a message of condolence to Bangladesh, condemning "barbarous acts" that were "offences against God and humanity," the Vatican said.