CIUDAD JUAREZ, Mexico -- In a moment filled with powerful political symbolism, Pope Francis prayed Wednesday at Mexico's dusty northern border for the thousands of migrants who have died trying to reach the United States and appealed for governments to open their hearts, if not their borders, to the "human tragedy that is forced migration."

"No more death! No more exploitation!" he implored.

It was the most poignant moment of Francis' five-day trip to Mexico and one of the most powerful images in recent times: History's first Latin American pope, who has demanded countries welcome people fleeing persecution, war and poverty, praying at the border between Mexico and El Paso, Texas, at a time of soaring anti-immigrant rhetoric in the U.S. presidential campaign.

Francis stopped short of calling for the U.S. to open its borders during a Mass celebrated just yards (meters) from the frontier. But in his homily, beamed live into the Sun Bowl stadium on the El Paso side, Francis called for "open hearts" and recognition that those fleeing gangland executions and extortion in their homelands are victims of the worst forms of exploitation.

"We cannot deny the humanitarian crisis which in recent years has meant the migration of thousands of people, whether by train or highway or on foot, crossing hundreds of kilometres through mountains, deserts and inhospitable zones," he said. "They are our brothers and sisters, who are being expelled by poverty and violence, drug trafficking and organized crime."

Francis also praised the work of activists who "are on the front lines, often risking their own lives" to help those caught up in the migration crisis. "By their very lives, they are prophets of mercy," he said.

And then, in a pointed message, Francis added a politically charged greeting to the 30,000 people gathered in the Sun Bowl to watch the simulcast on giant TV screens.

"Thanks to the help of technology, we can pray, sing and celebrate together this merciful love which the Lord gives us, and which no frontier can prevent us from sharing," Francis said. "Thank you, brothers and sisters of El Paso, for making us feel like one family and the same Christian community."

Immigrants gathered in El Paso said they were greatly moved by the words of Francis, who flew back to Italy after the Mass.

Angelica Ortiz, who was among some 500 people who were invited to be on the U.S. side, could barely speak after the pope's prayer. "I'm overcome by emotion," she said, "a lot of emotion."

People at the Mass also expressed happiness with the pope's message.

Wiping away tears, Angeles Arevalo said the pontiff's call for compassion toward migrants would be heard on both sides of the border. "They are watching us from there as well," she said, alluding to the simulcast in El Paso.

Marielena Torres also felt Francis' words could bring changes in attitudes about immigration: "He is the Holy Father, and he can help a lot."

Francis, the son of Italian immigrants to Argentina, had wanted to cross the border in solidarity with other migrants when he visited the U.S. last fall. That wasn't possible for logistical reasons, so he did the next best thing Wednesday by coming within a stone's throw of the fence to pray and lay a bouquet of flowers next to a large crucifix that is to remain at the site as a monument to his visit.

While migrant activists on both sides of the border cheered the gesture, Republican presidential hopeful Donald Trump criticized it as a politicized and ill-informed move.

"I don't think he understands the danger of the open border that we have with Mexico," Trump said in an interview last week with Fox television. "I think Mexico got him to do it because they want to keep the border just the way it is. They're making a fortune, and we're losing."

He and fellow GOP hopeful Sen. Ted Cruz have vowed to expel all the estimated 11 million immigrants in the U.S. illegally and build a wall along the border from Texas to California.

Asked to comment on the criticism, the Vatican spokesman, the Rev. Federico Lombardi, said the pope is concerned about the plight of migrants everywhere, not just in the United States.

"The pope always talks about migration problems all around the world, of the duties we have to solve these problems in a humane manner," Lombardi said Tuesday.

The Mass, celebrated in a field along a highway that parallels the Rio Grande, marked the climactic end of Francis' five-day swing through some of Mexico's most marginalized places, where drug-fueled violence has soared thanks to the complicity of police and other public institutions. Francis took both church and state to task for failing their people and urged the next generations to resist the lure of the drug trade.

In a speech Wednesday to workers and employers, Francis warned that without job opportunities, Mexico's youth risk being seduced into the drug trade. "Poverty becomes the best breeding ground for the young to fall into the cycle of drug-trafficking and violence," he said.

He urged employers to think instead of the Mexico they want to leave for their children.

"Do you want to leave them the memory of exploitation, of insufficient pay, of workplace harassment?" he asked. "What air will they breathe? An air tainted by corruption, violence, insecurity and suspicion or, on the contrary, an air capable of generating alternatives, renewal and change?"

"God will hold today's slave-drivers accountable," he warned.

Francis began his final day at Ciudad Juarez's Prison No. 3, where he told about 700 inmates at a chapel that they cannot undo the past but must believe that things can change. They all have the possibility of "writing a new story and moving forward," Francis said.

His message of hope came days after 49 inmates died in a riot at different prison in northern Mexico prison, where prisoners fought with hammers and makeshift knives. Eight more were injured Tuesday in a brawl at yet another prison.

Not long ago Juarez was the murder capital of the world as cartel-backed gang warfare fed homicide rates that hit 230 per 100,000 residents in 2010. A rash of killings of women, many of them poor factory workers who just disappeared, attracted international attention.

Times have changed, though. Last year, the city's homicide rate was about 20 per 100,000 people, roughly on par with Mexico's nationwide average of 14 per 100,000 -- and well below current hotspots of drug violence, such as the Pacific resort city of Acapulco and surrounding Guerrero state.

Many businesses that closed during Juarez's darkest years have reopened. Tourists are again crossing over from the United States and people say they no longer have to leave parties early to avoid being on the streets after dark.

"At least now we can go out. We can walk around a little more at that time of night," said resident Lorena Diaz, standing under a huge banner of Francis hanging from her balcony.

Diaz, who along with about 30 family members secured tickets for Wednesday's Mass, welcomed Francis' calls for Mexicans not to tolerate corruption and violence.

"He's telling us to get out of the trenches, not to close ourselves off," she said.


Associated Press writers Peter Orsi in Mexico City and Astrid Galvan in El Paso, Texas, contributed to this report.