(AP) -- Standing before Congress, Pope Francis issued a ringing call to action on behalf of immigrants Thursday, urging lawmakers to embrace "the stranger in our midst" as he became the first pontiff in history to address a joint meeting of the legislators.

Referencing the migration crisis in Europe as well as the United States' own struggle with immigration from Latin America, Francis summoned lawmakers "to respond in a way which is always humane, just and fraternal."

"We must not be taken aback by their numbers, but rather view them as persons, seeing their faces and listening to their stories, trying to respond as best as we can to their situation," Francis urged.

He was welcomed enthusiastically to a House chamber packed with Supreme Court justices, Cabinet officials, and lawmakers of both parties, uniting the bickering factions before he even opened his mouth as all stood to cheer his arrival. The sergeant at arms intoned "Mr. Speaker, the pope of the Holy See" and Francis made his way up the center aisle in his white robes, moving slowly as lawmakers applauded, some inclining their heads in bows.

Thursday's speech was the latest highlight for the pope's whirlwind three-day visit to Washington, the first stop on a three-city U.S. tour.

On Wednesday he was cheered by jubilant crowds as he visited the White House -- where he and President Barack Obama embraced each other's warnings on climate change -- paraded through Washington streets in his "popemobile," addressed U.S. bishops, noting the clergy sex abuse scandal, and celebrated a Mass of Canonization for Junipero Serra, the Spanish friar who founded major California missions.

Late Thursday, he moves on to New York and then later in the week to Philadelphia.

Introducing himself at the Capitol as "a son of this great continent," the Argentine pope, reading his remarks slowly in English, spoke from the same dais where presidents deliver their State of the Union speeches. Behind him sat Vice President Joe Biden and House Speaker John Boehner, the first and second in line to the presidency, both Catholics. Outside, tens of thousands watched on giant screens erected on the Capitol's West Lawn, and many more were watching on TV around the world.

Lawmakers of all political backgrounds and religious affiliations eagerly welcomed the pope, pledging to pause from the bickering and dysfunction that normally divide them and hear him out. Yet Francis spoke to a Congress that has deadlocked on immigration legislation -- at a time when there are more than 11 million people in the U.S. illegally and when some lawmakers have balked at Obama administration plans to accept more of the migrants from Syria and elsewhere who are now flooding Europe.

Indeed, Francis arrived at a moment of particular turmoil for Congress, with a partial government shutdown looming next week unless lawmakers can resolve a dispute over funding for Planned Parenthood related to the group's practices providing fetal tissue for research. Boehner himself, who invited Francis to speak and met with him privately beforehand, is facing a brewing revolt from tea party members who've threatened to force a floor vote on whether the speaker can keep his job.

Francis steered clear of such controversies, alluding only in passing to the Catholic Church's opposition to abortion when he noted, to applause, "our responsibility to protect and defend human life at every stage of its development."

He advocated abolition of the death penalty, something that enjoys widespread support from a number of lawmakers of both parties at the federal level, and spoke out against fundamentalism of all kinds, while urging care in combating it.

"A delicate balance is required to combat violence perpetrated in the name of a religion, an ideology or an economic system, while also safeguarding religious freedom, intellectual freedom and individual freedoms," Francis said.

On immigration, Francis urged lawmakers -- and the United States as a whole -- not to be afraid of migrants but to welcome them as fellow human beings, not things that can be discarded just because they are troublesome.

Francis, the son of Italian immigrants to Argentina, recalled that the America itself was founded by immigrants, that many lawmakers are descended from foreigners and that that new generations must not "turn their back on our neighbors."

Given an ovation when he spoke of the Golden Rule, he said, "Let us treat others with the same passion and compassion with which we want to be treated."

Francis has made migration the top priority of his pontificate. His first trip outside Rome as pope was to the Sicilian island of Lampedusa, Ground Zero of Europe's migration crisis where some 365 migrants drowned within view of shore in October 2013. He has decried the "inhuman" conditions facing migrants crossing the U.S.-Mexico border and encouraged frontier communities to not judge people by stereotypes but rather welcome migrants and work to end discrimination.

Recently, he called on all parishes and religious orders around the world to take in refugee families, and matched his call by hosting two such families in the Vatican. On his way to the airport last Saturday, he called on the Syrian family of four who had recently taken up residence in a Vatican flat. The experience was humbling, he said later: "You could see the pain in their faces."

On Thursday, security was tight outside the Capitol, with streets blocked off and a heavy police presence that rivaled an Inauguration or State of the Union address by the U.S. president. The scene on the West Lawn was festive but orderly, as thousands awaited the pope's appearance on the House Speaker's Balcony after his speech to Congress.

Libby Miller of Frederick, Maryland, said her friends all told her she was crazy for going to Capitol Hill with her 4-year-old son, Camden, and 2-year-old daughter, Avery. Miller, armed with toys, snacks and a sippy cup, found a spot on the Capitol lawn and said she wanted her kids to be there for an important moment in history. They won't understand it now, she said, but "they'll get it eventually."

Ahead of Francis' remarks lawmakers of both parties had busily sought political advantage from his stances, with Democrats in particular delighting in his support for action to overhaul immigration laws and combat global warming and income inequality. One House Republican back-bencher announced plans to boycott the speech over Francis' activist position on climate change, which the pontiff renewed alongside President Barack Obama on Wednesday.

But Boehner, a Republican and a former altar boy who invited the pope to speak after trying unsuccessfully to lure the two previous pontiffs to the Capitol, has dismissed concerns that the politically engaged Francis will stir the controversies of the day.

"The pope transcends all of this," said Boehner, who met on his own with Francis before the speech. "He appeals to our better angels and brings us back to our daily obligations. The best thing we can all do is listen, open our hearts to his message and reflect on his example."

Francis enjoys approval ratings the envy of any U.S. politician as he's remade the image of the Catholic Church toward openness and compassion, yet without changing fundamental church doctrine. Addressing a chamber full of elected officials Thursday, he may be the most adept politician in the room.

After speaking in the House chamber Francis was to stop by the Capitol's Statuary Hall and its statue of Father Serra, the 18th-century missionary whom Francis elevated to sainthood Wednesday in the first canonization on U.S. soil.

Later, he planned to stop at St. Patrick's Catholic Church and the Catholic Charities of the Archdiocese of Washington, before leaving for New York for more prayer services and a speech to the United Nations.