Francis told tourists and pilgrims in St Peter's Square that "the commandment 'do not kill' holds absolute value and applies to both the innocent and the guilty."
He added that there is "an ever more widespread opposition in public opinion to the death penalty, even only as an instrument of legitimate social defense."
"I appeal to the conscience of those who govern so that international consensus is reached for the abolishment of the death penalty," the pope said. "And I propose to all those among them who are Catholic to make a courageous and exemplary gesture: may no execution sentence be carried out in this Holy Year of Mercy."
The pope is building on church teaching, laid out by St John Paul II, that there's no justification for capital punishment.
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"In effect, modern societies have the possibility to efficiently repress crime without taking away definitely the possibility to redeem oneself from those who committed" the crime, Francis said.
The pope said "even criminals hold the inviolable right to life" given by God.
Francis called on all Christians and all those of good will to work not only to abolish capital punishment but also to improve prison conditions.
While the pope insists he doesn't interfere in the political sphere, he has also made clear people must follow what he calls a "well-informed" conscience, and that local bishops can give guidance to Catholics, including voters, on political issues.