Pope Francis has criticized the Trump administration's policy of separating migrant families at the Mexican border, saying populism is not the answer to the world's immigration problems.
Speaking to Reuters, the Pope said he supported recent statements by US Catholic bishops who called the separation of children from their parents "contrary to our Catholic values" and "immoral."
"It's not easy, but populism is not the solution," Francis said on Sunday night.
The comments came in a rare, wide-ranging interview in which he reflected on his five years as pontiff.
One of his most pointed messages concerned President Donald Trump's zero-tolerance immigration policy, in which US authorities plan to criminally prosecute all immigrants caught crossing the Mexican border illegally, holding adults in jail while their children are sent to government shelters.
The policy has caused an outcry in the United States and has been condemned abroad as videos emerged of youngsters held in concrete-floored enclosures and an audio of wailing children went viral.
US Catholic bishops have joined other religious leaders in the United States in condemning the policy.
"I am on the side of the bishops' conference," the pope said, referring to two statements from US bishops this month.
"Let it be clear that in these things, I respect (the position of) the bishops conference."
Francis' comments add to the pressure on Trump over immigration policy. The pope heads a church which has 1.3 billion members worldwide and is the largest Christian denomination in the United States.
The president has strongly defended his administration's actions and cast blame for the family separations on Democrats.
"Democrats are the problem," Trump said on Twitter on Tuesday. "They don’t care about crime and want illegal immigrants."
The US crackdown chimes with a new political mood sweeping western Europe over the large numbers of migrants and asylum-seekers, most of them escaping conflict and poverty in the Middle East and Africa.
The pope said populists were "creating psychosis" on the issue of immigration, even as aging societies like Europe faced "a great demographic winter" and needed more immigrants.
Without immigration, he added, Europe "will become empty."
He had other criticisms of the American president.
Francis said he was saddened by Trump's decision last year to implement new restrictions on American travel and trade with Cuba. The move rolled back his predecessor President Barack Obama's opening to the island nation. That deal, which the Vatican helped broker, "was a good step forward", the pope said.
He also said Trump's decision to pull out of the Paris agreement to curb climate change caused him "a bit of pain because the future of humanity is at stake". The pope said he hoped Trump would re-think his position.