Pope Leo calls out 'delusion of omnipotence' fueling Iran war in vigil for peace at St. Peter's Basilica

"Enough of the idolatry of self and money. Enough of the display of power. Enough of war," he wrote. "True strength is shown in serving life."

The archbishop of Tehran, Belgian Cardinal Dominique Joseph Mathieu, was among those in the pews.

Leo’s words came on the same day Vice President JD Vance and a U.S. delegation began face-to-face talks with Iran amid an uneasy ceasefire.

They were some of the first American pontiff’s strongest words yet after he called President Donald Trump’s threat against Iran on Tuesday "truly unacceptable."  

"Today, as we all know, there has also been this threat against the entire people of Iran, and this is truly unacceptable," the pope said earlier this week. "There are certainly issues of international law here, but even more so a moral issue for the good of the whole entire population."

Trump had written on Truth Social "A whole civilization will die tonight, never to be brought back again. I don’t want that to happen, but it probably will... God Bless the Great People of Iran!"

Hours later, the president announced a two-week ceasefire subject to Iran agreeing to "the COMPLETE, IMMEDIATE, and SAFE OPENING of the Strait of Hormuz," the president wrote in another post.

As the high-stakes talks began on Saturday in Islamabad, Trump told reporters outside the White House: "We win regardless of what happens. Maybe they make a deal, maybe they don’t."

For more than a month, the pope limited his remarks to muted appeals for peace, but in his Easter blessing last Sunday, he urged "those with weapons lay them down. Let those who have the power to unleash wars choose peace."

Leo also invoked what he said were the final words that Pope Francis issued to the world from the same balcony one year ago, during which the late pontiff warned of a "globalization of indifference."

"What a great thirst for death, for killing we witness each day in the many conflicts raging in different parts of the world," Leo said, quoting Francis.

Fox News' Jasmine Baehr and The Associated Press contributed to this report.