Pope Francis - on a visit to the South American country - also called on Colombians to forgive.

"Even if conflicts, violence, or feelings of revenge continue, we must not prevent justice and compassion from embracing each other, and thus absorb the suffering of Colombia," Francis said. 

Speaking in the former stronghold of the drug cartel run by Pablo Escobar, he called for a healing of pain and urged people "to take in every person who has committed crimes, confessed them, repented and committed himself to reparation and have him contribute to the construction of the new order."

The pope also thanked soldiers and policemen for helping overcome the violence that took place during more than five decades of conflict against the Revolutionary Armed Forces of Colombia (FARC).

In a meeting in Medellin with priests, seminarians and nuns, Francis spoke of the "drug assassins" who had converted Colombia's second-largest city into the murder capital of the world.

Medellin "evokes for me the many young lives cut short, discarded and destroyed" by drugs, he said. "I invite you to remember and accompany this mournful procession and ask forgiveness for those who destroyed the dreams of so many young people."

Before becoming pope, Francis was known for ministering to addicted youth in the slums of Buenos Aires.

After the Mass, Francis went to a century-old orphanage for abandoned girls.

jbh/sms (AP, dpa)