ABOARD THE PAPAL PLANE (RNS) — Pope Leo XIV said the war in Iran does not qualify as a “just war” according to Catholic teaching.

“I believe it has been already declared clearly,” Leo said while answering questions from journalists aboard the papal plane for his six-day visit to Spain.

“There is no just war there,” he said, referencing the conflict in Iran.

The question referred to U.S. Vice President JD Vance’s remarks in April, where he used just war theory to justify the war in Iran. On that occasion, Vance said the pope should “be careful” when talking about theology.

“When the pope says that God is never on the side of people who wield the sword, there is more than 1,000-year tradition of just war theory,” he said. President Donald Trump later said Leo was “weak” on war in a post on Truth Social.

Leo pointed to his most recent encyclical, “Magnifica Humanitas” (Magnificent Humanity), which says that just war theory has “too often been used to justify any kind of war” and is “now outdated.”

“The problem is that the just war theory comes from centuries past when we couldn’t imagine the weapons, human beings’ ability for destruction,” Leo said.

The document urges alternative ways to overcome conflict — “dialogue, diplomacy and forgiveness” — condemning the use of force which disproportionately harms civilians.

The pope has made “overcoming the theory of the ‘just war'” one of the themes of the first summit of cardinals he convened at the Vatican June 26-27, called a consistory.

It wasn’t the first time Pope Leo has spoken out against the war in Iran. He has issued repeated appeals for peace and dialogue since the conflict began in February.

Aboard the plane on Saturday, Leo also weighed in on the war in Ukraine, especially after Russian President Vladimir Putin recently refused to meet with Ukrainian President Volodymyr Zelenskyy. “I am worried for Ukraine,” Leo said. “We must really push to reach an end to the conflict and the war and find a solution,” he added, calling for continued negotiations.

“Already, four years and a half have passed. We must reach a solution,” he said, recognizing the United States’ efforts to mediate a peace.

The pope also said he is in contact with religious leaders in Lebanon, whom he met when he visited the country in November. “The situation is very complex,” he said, as Israel continues its offensive in the southern part of the country.

This story was produced via a collaboration between NPR and Religion News Service.