They made their appeal after an intensely emotional visit with hundreds of the detained refugees, many of whom were bawling openly. One man collapsed at the pope's feet, shaking while he cried for a blessing. A woman pleaded for medical care for a daughter with bone cancer.

Several others grabbed Francis' arms, hands, feet -- whatever was nearest -- screaming out for some sort of help or prayer.

In a joint declaration signed during the visit, the leaders sharply proclaim: "We appeal to all followers of Christ to be mindful of the Lord’s words, on which we will one day be judged."

Quoting Jesus' words in Matthew's Gospel, they state: "Assuredly, I say to you, inasmuch as you did it to one of the least of these my brethren, you did it to me."

In the declaration, signed at a center housing some 2,500 refugees -- where the walls had been whitewashed and the barbed wire removed for the high-level visit -- Francis, Bartholomew and Ieronymos say they had traveled together to demonstrate "profound concern" for the migrants' treatment.

"The tragedy of forced migration and displacement affects millions, and is fundamentally a crisis of humanity, calling for a response of solidarity, compassion, generosity and an immediate practical commitment of resources," they state.

"From Lesbos, we appeal to the international community to respond with courage," they continue. "We call upon all political leaders to employ every means to ensure that individuals and communities ... enjoy the fundamental right to live in peace and security."

The three leaders' joint trip to Europe's outer periphery, while described by the Vatican as "strictly humanitarian and ecumenical," appears as an almost unprecedented unified Christian push for politicians to do more in the face of the continuing refugee crisis.

The symbolism of the unified visit -- with Francis traveling east, Bartholomew traveling west, and Ieronymos welcoming them to his home country -- would have been nearly unimaginable even 15 years ago, when Pope John Paul II became the first pontiff to visit a Greek archbishop in more than a millennium.

Ieronymos, the archbishop of Athens and All Greece, pointed to the political dimension to the trip in remarks to refugees staying at the Moria camp, where the three leaders visited at mid-day Saturday.

The archbishop said that in seeing the eyes of children living there one can "immediately recognize ... the 'bankruptcy' of humanity and solidarity that Europe has shown these last few years."

In brief remarks to journalists aboard the papal plane from Rome, Francis said that this trip is different from those he normally takes abroad.

"This is a trip marked by sadness," said the pontiff. "We are going to meet the greatest humanitarian crisis since the Second World War."

"We will see many people who suffer and don't know where to go, who had to escape," he said, speaking also of the refugees who have died trying to reach Europe and adding: "We are going also to a cemetery, the sea."

Lesbos, six miles off the west coast of Turkey but about 150 miles off the east coast of mainland Greece, has become a key waypoint for refugees escaping violence or persecution in the Middle East. Of the more than a million migrants estimated to have traveled to the EU last year, about half have landed on the island's beaches.--NCR