ANNABA, Algeria - Pope Leo paid homage to his spiritual roots on Tuesday, travelling to the ancient birthplace in Algeria of St. Augustine of Hippo, who inspired him to become a priest.

The first American pope has drawn the ire of U.S. President Donald Trump after sharply criticising the Iran war. In honouring Augustine, Leo was highlighting a personal connection to a major figure of the early Church who first proposed criteria to evaluate whether wars could be considered just.

Augustine, who died in the year 430, said wars should only be waged in order to defend against aggression or protect the innocent, with the intention of restoring a state of peace and never out of a desire for cruelty.

Those criteria, with updates, remain Catholic doctrine. They have been invoked by some critics of the Iran war to argue that the conflict, started by surprise U.S.-Israeli airstrikes against Iran on February 28, is unjust.

Washington Cardinal Robert McElroy is among those critics. He said on Sunday that the war was "morally illegitimate", citing Augustine's principles.

Leo, who is on an ambitious, 10-day tour of four African countries, told Reuters on Monday that he planned to keep criticizing the war, despite Trump's comments.

He did not offer remarks on Tuesday as he visited the remnants of the city of Hippo, now Annaba, on Algeria's northeast coast. Under light rain, he laid a wreath of yellow and white roses and helped several Algerian Muslim Scouts in tan uniforms plant a sapling.

At a later meeting on Tuesday at a nearby nursing home run by Catholic sisters, the pope, a member of the Augustinian religious order, spoke out again.

"God's heart is torn apart by wars, violence, injustice and lies," Leo told the residents of the Little Sisters of the Poor home. "Our Father's heart is not with the wicked, the arrogant or the proud."

-Reporting by Joshua McElwee; Editing by Robbie Corey-Boulet and Alex Richardson/Reuters