The pope, who this week denounced violence in the name of religion - declaring "there is no God of war" - met 180 people who were wounded, or left traumatised or bereaved by the July 14 attack in Nice which claimed 86 lives.
"We need to start a sincere dialogue and have fraternal relations between everybody, especially those who believe in a sole God who is merciful," he said, speaking in the Vatican's giant Paul VI audience hall, and calling this "an urgent priority."
"We can only respond to the Devil's attacks with God's works which are forgiveness, love and respect for the other, even if they are different," he said.
Members of 58 families were flown in especially from the French Rivera resort city of Nice.
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They were joined in Rome by 150 others who travelled from France by car and a delegation from a French regional interreligious group, including the Catholic bishop of Nice and Muslim, Jewish, Orthodox and Protestant representatives.
While speaking out against violent acts carried out in the name of any god, Francis this week reminded the West that there were parts of the world being flattened by fighting.
Speaking in the Italian town of Assisi on Tuesday he said, "We are frightened... By some terrorist acts", but "this is nothing compared to what is happening in those countries, in those lands where day and night bombs fall."
"I don't sleep at night. The whole scene of the lorry moving, the mutilated bodies, decapitated, the entrails," he said.
The 49-year-old has decided to create a local association to support the victims of that awful night.
French police on Tuesday arrested eight associates of Mohamed Lahouaiej Bouhlel, a 31-year-old Tunisian, who rammed a 19-tonne truck through a crowd of more than 30,000 people on the seafront Promenade des Anglais on July 14 before police shot him dead.