Pope Francis arrived in Rome early Monday after a whirlwind tour of the United States, which included a farewell ceremony inside an airport hangar attended by Vice President Joseph Biden.

In an overnight tweet, the pope said: "With my heartfelt thanks. May the love of Christ always guide the American people! #GodBlessAmerica."

Before boarding his American Airlines jetliner in Philadelphia Sunday night, the pontiff expressed gratitude for his visit to the United States, which he called "days of great grace for me."

The pope's plane, dubbed "Shepherd One," left at 7:46 p.m. -- earlier than the scheduled 8 p.m. departure -- capping a nine-day tour of Cuba and the United States, with stops in Havana, Washington, New York City and Philadelphia.

The pope, who arrived at the airport earlier than scheduled, greeted Biden and his wife, Jill Biden, shaking their hands right before the start of the formal departure ceremony, which also was attended by Pennsylvania Gov. Thomas Wolf, Philadelphia Mayor Michael A. Nutter, Archbishiop of the Archdiocese of Philadelphia Charles J. Chaput and other officials. He met with organizers and volunteers with the World Meeting of Families before departing.

Chaput told the pope: "The heart of the people of the City of Brotherly Love are with you. We hate to see you leave. We're so grateful that you came to our home, Philadelphia."

The pope, in his brief remarks at the airport, also asked the vice president to "renew my gratitude" to President Obama and Congress.

"This land has been blessed with tremendous gifts and opportunities. I pray that you may all be good and generous stewards of the human and material resources entrusted to you."

He also mentioned his visit to Ground Zero, saying: "I was also very moved to stand with my brothers and sisters of other religions at Ground Zero, that place which speaks so powerfully of the mystery of evil."

Francis ended his speech by saying, "God bless America."

Betty Trymbiski of Doylestown, Pennsylvania, was given tickets to attend the pope's departure Thursday by a friend.

"Other than getting married and having my four sons, this is one of the most amazing things that's ever happened to me," she said.

"He's a people's pope. You really can relate to him. He's just a regular guy. I think I'm closer to him than any other pope we've had."

The airport reception served Argentine food, Thai noodles and chicken skewers.

The last day of his trip included a visit with prison inmates and a ride in his popemobile along Benjamin Franklin Parkway, during which he waved to crowds and kissed at least a dozen babies and young children.

The pope ended his U.S. tour with a late afternoon Mass estimated to have been attended by hundreds of thousands of people for the conclusion of the World Meeting of Families.

He also waded into one of the Catholic church's most devastating controversies: the priest sexual abuse scandal. The pope met with a small group of victims and afterward said of the abuse, "God weeps."

The pope vowed "careful oversight" to ensure the protection of young people and said in comments to church officials after the meeting with victims those responsible for the abuse would be held accountable.

"The people who had the responsibility to take care of these tender ones violated that trust and caused them great pain," he said. "Those who have survived this abuse have become true heralds of mercy. Humbly we owe each of them our gratitude for their great value, as they have had to suffer terrible abuse, sexual abuse of minors," he said.

The 78-year-old pontiff kept a busy schedule throughout his trip, meeting with President Barack Obama at the White House, addressing a joint session of Congress and visiting the September 11 Memorial & Museum in lower Manhattan.

Along the way, the pope also met with plenty of regular people, leading a procession through Central Park and visiting a Catholic school in East Harlem. His pastoral style showed through, with Francis offering embraces and hugs, and delighting crowds.

His words, many said, offered hope.

The Argentine-born pontiff repeatedly mentioned his roots as the son of an immigrant, while calling for compassion for immigrant families in the United States, at a time when the issue of illegal immigration has become a divisive political issue.

In a speech to the UN General Assembly, the pope called for the world's attention to pivot to climate change.

"In effect, a selfish and boundless thirst for power and material prosperity leads both to the misuse of available natural resources and to the exclusion of the weak and disadvantaged," the pope said.