Pope Francis said a prayer of remembrance and addressed religious leaders at an interfaith ceremony at the September 11 Memorial in downtown Manhattan, as he continued his tour of New York Friday.

The pope arrived to cheers from the gathered crowd, and walked toward the two massive waterfall pools that mark the footprints of the World Trade Center's twin towers before they were destroyed in the 2001 terrorist attacks.

He shook hands with former New York Mayor Michael Bloomberg and began speaking with some 18 people from 10 victims' families.

In his remarks, Pope Francis asked God for eternal peace for those killed as well as healing for the relatives of the nearly 3,000 people lost in the 2001 terror attacks in New York, at the Pentagon and in a field in Pennsylvania.

And he prayed to God to bring "peace to our violent world" and to "turn to your way of love" those who justify killing in the name of religion.

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Francis visited the museum after a speech at the United Nations Friday morning in which he condemned ethnic violence and the destruction of the environment.

Religious leaders --including Jewish, Muslim, Greek Orthodox, Hindu and other faiths – also spoke to more than 400 representatives from faith groups on the need for peace.

The pope spoke near the underground flood wall that separates lower Manhattan from the Hudson River and held fast during the 2001 terrorist attacks. The wall sits just next to what is known as the "Last Column," the final steel beam removed during the recovery after the attacks.

Security for the pope's U.N. visit was exceedingly tight. Longtime staffers agree it was even tighter than for the annual ministerial meeting of the U.N. General Assembly, which brings at least 120 world leaders to U.N. headquarters

Whole areas of the headquarters were declared off-limits. Long curtains were hung on windows overlooking the East River and First Avenue, apparently to thwart any snipers.

Hundreds of U.N. security officers and New York City police, as well as Secret Service agents, bomb-sniffing dogs and police boats, were on duty.

Francis' afternoon schedule reflected the penchant of the "people's pope" for engaging with the public, starting with a visit to Our Lady Queen of Angels School, set amid public housing in the heavily Hispanic neighborhood of East Harlem.

After the morning's deadly serious activities, the 78-year-old pope clearly perked up when he got to the Catholic school. He joked around with the children, chatted happily with them in Spanish, shook hands and posed for a few selfies. A security guard intervened when one girl gave him a big hug.

The pope — who says he hasn't watched TV in decades and doesn't know how to work a computer — even got a lesson in how to use a touchscreen from fourth-grader Kayla Osborne, 8.

The crowd in the gym included about 150 immigrants and refugees, some of them in the U.S. illegally.

In his remarks, Francis recalled the Rev. Martin Luther King Jr.'s "I Have a Dream" speech, saying: "His dream was that many children like you could get an education. It is beautiful to have dreams and to be able to fight for them."

About a half-hour before the popemobile passed through Central Park, a rainbow suddenly appeared above the crowd, which erupted in joyous "Oooohs!" and "Ahhhhhs!"

Francis smiled as he rode slowly in his open-sided Jeep past a cheering, shrieking crowd and a sea of arms holding cellphones aloft. For those lucky enough to score a ticket, there was a catch: No backpacks, no chairs and no selfie sticks.

Denise Villasenor, a 27-year-old Columbia University graduate student from the Philippines and a Catholic, practiced capturing a selfie with the pope ahead of the procession.

"The pope's positions always revolve around compassion and love — you know, being a person for others," she said. "Immigration, the environment, it all comes to being compassionate, for others."

Next on the itinerary was the processional drive through Central Park, the most public event for the pope while in New York. Some 80,000 people received tickets to watch Francis in his open-sided Jeep popemobile.

The processional was added to the pope's packed schedule to allow more people to see him, and vice versa.

He rode through part of the park in his open-sided Jeep popemobile, which he used in a short motorcade on Fifth Avenue on Thursday night.

Francis is known for his openness to interacting with people, and he sometimes wades into crowds to do so. Security is tight, with ticketholders banned from bringing chairs and other items.

One woman appeared to faint or fall in the crowd about an hour before he arrived. Emergency workers aided her, and she returned to the throng.

In the evening, he celebrated Mass at Madison Square Garden, usually the site of basketball games and rock concerts but this time the scene of a solemn service celebrating New York in all its diversity.

"Living in a big city is not always easy," Francis told 18,000 people at the Garden, easily one of the most respectful crowds the arena has ever seen. "Yet big cities are a reminder of the hidden riches present in our world in the diversity of its cultures, traditions and historical experiences."

He concluded the service with the customary "go in peace and serve the Lord" and added, "Please, I ask you, don't forget to pray for me."

On Saturday morning, the pope flies to Philadelphia for a big Vatican-sponsored rally for Catholic families. As many as 1 million people are expected for the final Mass on Sunday.

The Associated Press contributed to this report.