The spiritual leader of the world's Roman Catholics made the comment during a ceremony marking the feast day of St. Francis of Assisi, the church's patron saint of animals and the environment who was born in the town in the late 12th century, Vatican Radio reported.
People must respect creation and "each human being," the pope said to a crowd at St. Francis Square.
"Let us not be instruments of destruction!" he said.
"May there be an end to armed conflicts which cover the earth with blood, may the clash of arms be silenced and everywhere may hatred yield to love, injury to pardon, and discord to unity," Francis said.
"Let us listen to the cry of all those who are weeping, who are suffering and who are dying because of violence, terrorism or war."