Pope Francis has appealed to US lawmakers to help the poor, do more for suffering migrants around the world and fight climate change, during a historic speech to Congress.
A day after meeting President Barack Obama and enjoying a rapturous welcome from thousands of people on the streets of Washington, Francis became the first pontiff to address a joint session of the Senate and the House of Representatives.
Pope Francis wore flowing white vestments as he strode down to the front of the chamber to applause and a standing ovation.
He triggered another round of clapping from the hundreds of lawmakers, Supreme Court justices, cabinet ministers and Vice President Joe Biden by saying it was an honour to be in "the land of the free and the home of the brave."
The 78-year-old Pope addressed one of the most tragic crises of the day - the relentless flow into Europe of Africans, Afghans and people from the Middle East, mainly Syrians fleeing their country's ruinous war.
"Our world is facing a refugee crisis of a magnitude not seen since the Second World War," he said.
But the Argentine-born pontiff also spoke of the plight of poor Central Americans and Mexicans who make often deadly treks across the Mexican border into US states like California and Arizona.
"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 we can to their situation," he said. "To respond in a way which is always humane, just and fraternal."
To some extent, the Pope was speaking to deaf ears.
The Republican-controlled Congress has failed to approve a sweeping reform that would have helped the estimated 11 million people, mostly Latinos, living in the US without residency papers to gain legal status.
On climate change, the Pope alluded to his recent encyclical in which he denounced global warming as a woe caused by mankind.
"I am convinced that we can make a difference, I'm sure, and I have no doubt that the United States - and this Congress - have an important role to play. Now is the time for courageous actions and strategies," he said.
The Pope also called for a worldwide end to the death penalty - the US is one of the few countries that still practise it - and denounced the arms trade as being fuelled by hunger for "money that is drenched in blood."
After his speech, the Pope stepped out onto a balcony overlooking the National Mall and greeted tens of thousands of cheering well-wishers down below.
"Buenos dias," he said, eliciting a roar of approval - and asked God to bless the crowd. "Thank you very much and God Bless America!" he concluded.
Later on Thursday (local time) the Pope was to leave for New York, where he will address the United Nations on Friday.
He wraps up his six-day US trip on Saturday and Sunday in Philadelphia at an international festival of Catholic families.