Pope Francis says a "good part of humanity" would be destroyed by a major war between the United States and North Korea, and he suggested a third country should enter as a mediator between the two rivals.
Francis made the comments on April 29 aboard the papal plane as he was returning to Rome after a trip to Egypt.
Tensions have risen on the Korean Peninsula as North Korea continues to test ballistic missiles in defiance of United Nations regulations.
Pyongyang has also tested nuclear weapons and has indicated it is attempting to develop missiles capable of reaching the United States.
U.S. President Donald Trump, who has sent a naval strike force to the Korean Peninsula, has warned of "catastrophic" consequences if the world fails to stop North Korean leader Kim Jong Un's weapons program and has indicated military options remain on the table.
The pope said he would urge the U.S. president and other leaders to use diplomacy and negotiation "because it's the future of humanity."
He suggested a third country, such as Norway, could act as a mediator in the crisis.
"I call on, and will call on, all leaders, as I have called on leaders of various places, to work to seek a solution to problems through the path of diplomacy," he said.
"Today, a wider war will destroy not a small part of humanity, but a good part of humanity and culture," he said. "It would be terrible. I don't think humanity today could bear it."
Trump is due to visit Sicily on May 26-27 for a meeting of Group of Seven leaders.
The administration has not yet said if the president will be stopping in Rome to meet the pope, who said, "I receive every head of state who asks for an audience."
Francis's visit to Egypt follows the bombings of three Egyptian churches in recent months that have killed dozens of worshipers. The attacks were claimed by the Islamic State (IS) extremist group.
He held an open-air Mass for Egypt’s small Catholic community to show his support for Christians in the mainly Muslim Arab country that has often been the target of IS attacks.
"The only fanaticism believers can have is that of charity," the pope said at the service.
"Any other fanaticism does not come from God and is not pleasing to him!" he added.