“And separating children from their parents goes against natural law, and those Christians … they can’t do it either,” he added. “It’s cruel. It falls under the greatest of cruelties. And to defend what? The territory, or the country’s economy or who knows what.”

“I don’t know what happens when this new culture of defending territories by building walls enters. We already know one, [the one] from Berlin, that brought us a lot of headaches and a lot of suffering,” the leader of the Roman Catholic Church said.

The pope talked about the situation at the U.S.-Mexico border during an interview with Mexican news organization Televisa , also warning Trump against resuming his policy of separating migrant families.

Pope Francis said Tuesday that he is willing to personally tell President Donald Trump that it is wrong to build a border wall, as the pontiff continues to voice opposition to the president’s immigration policies.

When Televisa’s Vatican reporter asked if the pope would tell Trump the same thing to his face if the president were sitting in front of him, Francis said, “The same, because I say it publicly … I have even said that those who build walls end up being prisoners of the walls they build.”

Francis made the prisoners comment March 31, the weekend that the Trump administration announced it was cutting off aid to El Salvador, Guatemala and Honduras to punish their governments for the influx of migrants at the U.S.-Mexico border. In response to Trump’s threat to close the border, the pope said migration “must be resolved differently, humanely, not with razor wire.”

The Vatican also announced April 27 that the pontiff donated $500,000 in aid to migrants in Mexico who have sought a “better future in the United States” but have found the U.S. border “closed to them.” Pope Francis said the donation would be distributed to 27 projects across Mexico to help fund housing, food and other necessities to Central American migrants fleeing poverty and violence.

Trump has constantly peddled the idea that a wall at the border will help stem a flow of drugs and crime coming into the U.S., and the president has clashed with House Democrats and some judges on how to fund it. Trump met with the pope in 2017, and no further meeting is reportedly planned.

The pope has long been a critic of the president’s immigration policy and rhetoric. In 2016, Francis said a person who only thinks about building walls instead of bridges “is not Christian.”

In 2018, the pope criticized the Trump administration’s policy of separating children from parents who illegally crossed the southern border, a policy that was later reversed after an outpouring of criticism. Trump denied reports last month that he’s considering reinstating the policy.

During his Televisa interview, Francis also rejected criticisms from a group of ultra-conservative Roman Catholics who call him a heretic. The group began a petition earlier this month encouraging bishops to denounce Francis over several topics, including communion for divorced people and religious diversity.

Francis said Tuesday that he took the petition “with a sense of humor” and said that he prays for the group “because they are wrong, and … some of them are being manipulated.”