WASHINGTON, United States (AFP) – President Barack Obama and Pope Francis married their political and spiritual power to urge action on immigration and the environment yesterday, during the popular pontiff’s maiden White House visit.

America’s first black president offered the first Latin American pope a stately and effusive welcome on the South Lawn, praising his moral leadership on issues that politics has struggled to address.

“I believe the excitement around your visit must be attributed not only to your role as pope, but to your unique qualities as a person,” Obama told his guest.

“In your humility, your embrace of simplicity, the gentleness of your words and the generosity of your spirit, we see a living example of Jesus’ teachings, a leader whose moral authority comes not just through words but through deeds.”

Though Pope Francis has inveighed against the materialism that the United States seems to embody like no other, he is also a potential political ally for Obama, sharing many of his progressive goals and bringing along many of America’s 70 million Catholics.

Speaking in fluent but accented English, the 78-year-old Argentine pontiff returned the warm blessings of his host.

“As the son of an immigrant family, I am happy to be a guest in this country, which was largely built by such families.”

In a nod to Washington’s bitter debate about immigration reform, Francis said he would address Congress “to offer words of encouragement to those called to guide the nation’s political future in fidelity to its founding principles.”

Obama lauded Francis for reminding the world that “the Lord’s most powerful message is mercy.”

“That means welcoming the stranger with empathy and a truly open heart, from the refugee who flees war-torn lands to the immigrant who leaves home in search of a better life,” Obama said.

It is a joint message that may also resonate strongly in Europe, which has been convulsed for months by an ongoing refugee crisis.

Similarly, as many US conservatives question the very existence of man-made climate change, Francis and Obama made a de facto joint appeal for action on the issue.

“Holy Father, you remind us that we have a sacred obligation to protect our planet, God’s magnificent gift to us,” Obama said.

Francis took up the call.

“Accepting the urgency, it seems clear to me also that climate change is a problem which can no longer be left to a future generation,” Francis said.

“When it comes to the care of our ‘common home,’ we are living at a critical moment of history.”

The pope was afforded a full ceremonial welcome and an Oval Office meeting on his historic first visit to the United States, and to Washington – a political city that ordinarily shrugs its shoulders when presidents, queens and sheikhs roll through.