Pope Francis arrives to board his plane at Fiumicino airport to go to Panama city in order to participate to the World Youth Day 2019. Vincenzo Pinto / AFP/Getty Images

Pope Francis has said fear of migration is "making us crazy," as he begins a trip to central America amid a standoff over President Donald Trump's promised wall at the U.S.-Mexico border and a new caravan of migrants heading north.

Francis, asked by reporters en route to Panama Wednesday about the proposed border wall, responded: "It is the fear that makes us crazy."

Mr. Trump, meanwhile, reiterated his commitment to a border wall on Wednesday, offering the Republican party via tweet a "new theme" to tout until the wall is complete: "BUILD A WALL & CRIME WILL FALL."

BUILD A WALL & CRIME WILL FALL! This is the new theme, for two years until the Wall is finished (under construction now), of the Republican Party. Use it and pray! — Donald J. Trump (@realDonaldTrump) January 23, 2019

He is also expected to offer words of encouragement to young people gathered in Panama for World Youth Day, the church's once-every-three-year pep rally that aims to invigorate the next generation of Catholics in their faith.

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Pope's previous criticism of Trump policy

The Catholic Church's first Latin American pope and the son of Italian immigrants to Argentina, Francis has made the plight of migrants and refugees a cornerstone of his papacy.

The pope has previously agreed with U.S Catholic leaders, who called the Trump administration's "zero tolerance" policy on illegal border crossings "immoral" and opposed to the values of the church.

"A person who thinks only about building walls, wherever they may be, and not building bridges, is not Christian," Pope Francis said last year. "This is not in the Gospel."

Latest on the migrant caravan headed north

The migrant caravan of around 1,800 Central Americans made its way toward the U.S from Ciudad Hidalgo in Mexico earlier this week as CBS reporter, Adriana Diaz reported.

The group started crossing into Mexico last weekend, and the long line to enter stretches back to a bridge on the border. Thousands of migrants left Honduras a week ago after word about a new caravan spread on Facebook.

The orderly lines are a stark contrast to October's caravan, when an influx of migrants overwhelmed the Mexican government and created a bottleneck on the same bridge. Some jumped to swim to Mexico instead, and other migrants tore down a fence to gain entry.

Where there was once a fence, there's now a gate that is wide open. But migrants have to wait on a long line. It's the result of Mexico's new open-door migration policy that is just a week old.

Of the thousands of migrants that made it to the U.S. border in the last major caravan, less than 700 remain in Tijuana hoping for asylum.