CIUDAD JUÁREZ, Mexico — Stepping to the concrete edge of the Rio Grande, Pope Francis on Wednesday went to a militarized divide of the United States-Mexican border and prayed for compassion toward immigrants. He never set foot in the United States, but he did step directly, and deliberately, into the acrimonious American debate over immigration.

Beneath a brilliant blue sky, Francis turned the dusty no man’s land of the border into a media-saturated setting for a potent symbolic moment: On one side was a crowd of 200,000 people waiting for him to lead Mass in this Mexican border city. On the other was a small group of people from the Roman Catholic Diocese of El Paso, along with police officers and border guards, some peering at the spectacle through binoculars usually used to catch migrants trying to sneak over the border.

Francis slowly walked up to a sloped memorial that was built for his visit to commemorate those who have died along the Mexican border. He stood before a large cross overlooking the border fence, made the sign of the cross and prayed before laying a bouquet of flowers on a small table before the cross. Then he looked over to the United States and waved his hand to offer a papal blessing.