Pope Leo XIV said the war being waged by the United States and Israel against Iran was not a “just war”, arguing that the centuries-old theory no longer reflected the realities of modern warfare.

Speaking to journalists aboard his flight from Rome to Madrid during the fourth foreign trip of his pontificate, the pope was asked whether the conflict in Iran could be considered a just war after US Vice President JD Vance invoked the concept while defending Washington’s military actions against Tehran.

“There is no just war there,” Pope Leo said.

“The problem is that the just war theory comes from centuries ago, from a time when people could not imagine the weapons and destructive capacities that exist today,” he added.

The pontiff’s remarks come amid previously reported tensions with US President Donald Trump over the conflict in Iran.

As fighting continued, Pope Leo repeatedly called for an end to the war and criticised rhetoric that he said could fuel further escalation.

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Earlier this year, he described Trump’s threat that “there will be no civilisation left in Iran” as “unacceptable”.

Trump later responded by describing the pope as “weak and terrible on foreign policy”.

The pope rejected the criticism, saying he was not afraid and would continue speaking out against war.

The exchange also prompted reactions in Italy, where political leaders criticised Trump’s remarks and voiced support for the pope’s calls for peace.

Italian Prime Minister Giorgia Meloni described the comments directed at Pope Leo as “unacceptable”.