Francis made his remarks in his yearly speech to diplomats accredited to the Vatican, an overview of the world situation which has come to be known informally as his "state of the world" address.
Francis spoke of "the war in Ukraine, with its wake of death and destruction, with its attacks on civil infrastructures that cause lives to be lost not only from gunfire and acts of violence, but also from hunger and freezing cold".
He then immediately quoted from a Vatican constitution, saying "every act of war directed to the indiscriminate destruction of whole cities or vast areas with their inhabitants is a crime against God and humanity which merits firm and unequivocal condemnation".
Referring to the Cuban missile crisis in 1962, he said: "Sadly, today too, the nuclear threat is raised, and the world once more feels fear and anguish."
He repeated his appeal for a total ban on nuclear weapons, saying even their possession for reasons of deterrence is "immoral".
(Reporting by Philip Pullella; Editing by Ed Osmond)
