Pope Francis demanded Saturday that the world never forget the victims of the Ottoman-era slaughter of Armenians at the country's imposing genocide memorial, hours after drawing a standing ovation from his hosts when he declared the slaughter a planned "genocide" aimed at annihilating an entire people.

Francis laid a wreath at the memorial and stood, head bowed, in silent prayer before an eternal flame as priests blessed him with incense and a choir sang haunting hymns.

"Here I pray with sorrow in my heart so that a tragedy like this never again occurs, so that humanity will never forget and will know how to defeat evil with good," Francis wrote in the memorial's guest book. "May God protect the memory of the Armenian people. Memory should never be watered-down or forgotten. Memory is the source of peace and the future."

The scene was powerful: Francis took his place next to the Armenian Apostolic patriarch, Karekin II, and a gathering of black-hooded Orthodox bishops, shaded by the memorial's 12 slanted slabs of rock representing the 12 western provinces lost to Turkey after World War I. Later, he met with descendants of some of the 400 Armenian orphans taken in by Pope Pius XI and housed at the papal summer residence south of Rome in the 1920s.

After visiting the Tzitzernakaberd memorial, Francis headed to the northwestern city of Gyumri, where crowds filled a main square for his only public Catholic Mass of the three-day trip to Armenia. He was ending his day with a prayer for peace back in the capital Yerevan, for what the Vatican said would be the largest gathering of his visit.

The Vatican has long held the Armenian cause dear, holding up the poor nation of 3 million mostly Orthodox Christians as a bastion of faith and martyrdom in a largely Muslim region and the first nation in the world to adopt Christianity as a state religion in 301.

In the most carefully watched speech of the trip, Francis on Friday ad-libbed the politically charged word "genocide" to his prepared text, listing the Armenian genocide alongside the Holocaust and Stalinism as the three great mass slaughters of the 20th century.

There was no immediate reaction from Turkey, which withdrew its ambassador last year and accused Francis of spreading lies when he first termed the slaughter a genocide. Turkey rejects the term, saying the 1.5 million death figure cited by historians is inflated and that people died on both sides as the Ottoman Empire collapsed amid World War I.

"Sadly that tragedy, that genocide, was the first of the deplorable series of catastrophes of the past century, made possible by twisted racial, ideological or religious aims that darkened the minds of the tormentors even to the point of planning the annihilation of entire peoples," Francis said.

"It's so sad how, in this case and in the other two, the great international powers looked the other way," he added, referring to the subsequent horrors of Nazism and Stalinism.

In the run-up to the visit, the Vatican had refrained from using the term "genocide," mindful of Turkish opposition to the political and financial implications of the word given Armenian claims for reparations.

But Francis, never one to shy from speaking his mind, added the word at the last minute. President Serzh Sargsyan, Armenian political and religious leaders and the diplomatic corps in attendance gave him a standing ovation.

The Vatican spokesman, the Rev. Federico Lombardi, said Francis' declaration of a genocide must be taken in the context of recognizing a past horror to then move on in friendship and reconciliation. Lombardi denied that the Vatican's diplomatic speechwriters had intentionally left the word out, saying they had wanted to leave it up to the pope to decide what to say.

In a largely Orthodox land where Catholics are a minority, Armenians have seemed genuinely honored to welcome a pope who has long championed the Armenian cause from his time as an archbishop in Argentina and now as leader of the 1.2-billion strong Catholic Church. His 2015 declaration that the massacres were considered a "genocide" sealed their affection for him.

"I shook the pope's hand but didn't have the time to kiss it," 42-year-old Yerevan resident Nazik Sargsyan said Friday as Francis arrived. "I'm sure God's blessing has come down on me with that handshake."