Pope Leo appealed on Saturday for authorities in Iran and Israel to act with "reason" after recent airstrikes and to pursue dialogue.
He told an audience in St. Peter's Basilica he was following the situation with "great concern."
"In such a delicate moment, I strongly wish to renew an appeal to responsibility and to reason," said the pope.
"The commitment to building a safer world free from the nuclear threat must be pursued through respectful encounters and sincere dialog to build a lasting peace, founded on justice, fraternity, and the common good," he said.
"No one should ever threaten the existence of another," said Leo. "It is the duty of all countries to support the cause of peace, initiating paths of reconciliation and promoting solutions that guarantee security and dignity for all."