Pope Francis cited his immigrant roots and quoted Dr. Martin Luther King Jr. in delivering a powerful message Wednesday at the White House, calling for an end to discrimination and protection of the environment.

"Mr. President, together with their fellow citizens, American Catholics are committed to building a society which is truly tolerant and inclusive, to safeguarding the rights of individuals and communities, and to rejecting every form of unjust discrimination," the pope told President Barack Obama in welcoming remarks.

Addressing 11,000 ticketed guests on the South Lawn of the White House under clear blue skies, the pope and the president in their comments touched on many concerns they both share, including immigration, climate change, Syrian refugees and renewed U.S.-Cuban relations.

Before they spoke, the president and the pope stood side by side and listened to the national anthems of the Vatican and the United States.

The pope also praised Obama for proposing an initiative to reduce air pollution.

"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 to Obama.

The pope referred to his recent encyclical on the environment and said, "Such change demands on our part a serious and responsible recognition not only of the kind of world we may be leaving to our children, but also to the millions of people living under a system which has overlooked them."

"Our common home has been part of this group of the excluded which cries out to heaven and which today powerfully strikes our homes, our cities and our societies," the pope said. "To use a telling phrase of the Rev. Martin Luther King, we can say that we have defaulted on a promissory note and now is the time to honor it."

In his "I Have a Dream" speech at the Lincoln Memorial on Aug. 28, 1963, King had said that the words of the U.S. Constitution and the Declaration of Independence were "a promissory note" that "all men would be guaranteed the inalienable rights of life, liberty, and the pursuit of happiness."

"It is obvious today that America has defaulted on this promissory note insofar as her citizens of color are concerned ... ," King had said.

Francis began his address by citing his own immigrant roots in Argentina and underscored the role of immigration in creating and building the United States. He was touching on one of his favorite themes and a hot-button issue in the United States.

"As the son of an immigrant family, I am happy to be a guest in this country, which was largely built by such families," he said, speaking in English.

Francis also voiced his concern for religious freedom, calling it "one of America's most precious possessions."

He issued a call "to preserve and defend that freedom from everything that would threaten or compromise it."

Obama opened the White House welcome by telling the pope: "On behalf of the American people, it is my great honor and privilege to welcome you to the United States of America. Your message of love and hope has inspired so many people, across our nation and around the world."

"You remind us of the costs of war -- particularly on the powerless and defenseless and urge us toward the imperative of peace," the president said.

Obama concluded by saying, "May our generation heed your call to 'never remain on the sidelines of this march of living hope.'"

After the speeches and a hymn by the Saint Augustine Choir, Pope Francis and Obama briefly appeared on the White House's Truman balcony to wave to those on the lawn, prompting cheers and applause. They then retired to the Oval Office.

Shortly after 11 a.m., the papal motorcade -- this time in an open-top Jeep -- left the White House.

Earlier Wednesday, the pope left the apostolic nunciature, where he spent his first night in the Unites States, and headed right to the crowd that had gathered there to greet him.

Grinning widely, Francis went from one youngster to the next, shaking hands, kissing cheeks and exchanging hugs. He affectionately grabbed one young man by the back of the neck and touched his head.

Following his one-on-one with Obama, Francis will tour the Ellipse and parts of the National Mall in a papal parade, according to the White House website. Throngs of people lined up before dawn Wednesday in hopes of seeing the papal parade as he travels to St. Matthew's Cathedral to pray with American bishops.

After the pope's plane touched down at Joint Base Andrews Tuesday afternoon, Obama personally welcomed the pontiff to the United States, warmly shaking his hand as hundreds of admirers cheered.

It is the first visit to the United States for Francis and the fourth ever by a pope. He will take a six-day, three-city tour of the United States that will include addresses to a joint meeting of Congress, the United Nations and the World Meeting of Families in Philadelphia.

The pope is also scheduled to lead a midday prayer at the Cathedral of St. Matthew the Apostle and an afternoon Mass for the canonization of Junipero Serra, the Spanish missionary who founded the first nine of 21 missions in California. The ceremony will take place at the Basilica of the National Shrine of the Immaculate Conception.

His address before Congress -- the first time a pope will ever address that body -- is planned for Thursday morning. For the benefit of the public, the speech will be broadcast live on jumbotrons on the West Lawn of the Capitol, according to the White House website.

With Tom Brune and Olivia Winslow