On his penultimate day in Colombia, Francis flew to Medellin, the city northwest of the capital that was once notorious as the stomping grounds of drug lord Pablo Escobar.
In unscripted comments at the last event of the day, he said he could not leave without mentioning the "painful memory" of "so many young lives truncated, discarded, destroyed".
He asked his listeners to ask God "for forgiveness for those who destroyed the dreams of so many young people. Ask the Lord to convert their hearts, ask for an end to this defeat of young humanity."
The Medellin that Francis visited is a city transformed since his predecessor Pope John Paul visited in 1986. It was then rife with violence among cartels, paramilitary groups and guerrillas that raged in the poor "comuna" neighborhoods on its outskirts.
The city is now heralded as a model of urban development. It has installed cable cars up the steep Andean slopes that surround it to save working-class residents a punishing climb, and it has built libraries in sections that were once sites of gun battles.
Feared drug trafficker Escobar, Medellin's most infamous resident, was gunned down in the city in a U.S.-backed operation in 1993. He was recently resurrected as a character in the popular Netflix series "Narcos."
At the start of the day, Francis said a Mass where he urged Colombians to help their fellow citizens who hunger for food, dignity and God, pressing his appeal for the South American country to tackle social inequality.
Speaking in a homily to hundreds of thousands of people on muddied fields, Francis urged Colombians to "get involved" in helping each other and to embrace "acts of non-violence, reconciliation and peace."
The leader of the world's 1.2 billion Roman Catholics has brought a message of national reconciliation as the country tries to heal the wounds left by a 50-year civil war and bitter disagreements over last year's peace deal with leftist guerrillas that some say lets them off too leniently.
On Friday in the tropical city of Villavicencio, the pontiff asked Colombians skeptical of the deal with the FARC guerrillas to be open to reconciliation with those who have repented, speaking hours after a top rebel leader asked the pontiff for forgiveness..
Francis has also used his trip to the predominantly Roman Catholic country to denounce the social inequality that still plagues Colombia, which has extreme poverty in some rural areas.
He has called for laws to tackle the structural causes of these problems, which he said spur violence.
Christians, he told the ecstatic crowd at the Mass, "are called upon to be brave, to have that evangelical courage which springs from knowing that there are many who are hungry, who hunger for God - how many people hunger for God! - who hunger for dignity, because they have been deprived."
He visits the city of Cartagena on Sunday before leaving for Rome that night.
(Additional reporting by Helen Murphy and Anastasia Moloney in Bogota; Editing by Helen Murphy and Cynthia Osterman)
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)