Fr Karadima, an influential priest who was found guilty by the Vatican of sexually abusing young boys and ordered to do penance, shook the Catholic Church in Chile.
Pope Francis said on Mass for some 400,000 people in Santiago on Tuesday that he was sorry for the “irreparable harm” caused to the victims of sexual abuse by Church ministers.
He said “I know the pain of these cases of child abuse and I am following how much is needed to overcome this serious and painful evil”
Earlier on, Pope Francis has been criticised in Chile for a decision to ordain a bishop accused of covering up sexual abuse by a priest.
Francis has said in the past that dealing with abuse is vital for the Church’s credibility, and that “sanctions” must be imposed against perpetrators.
But critics in Chile say he failed to respond to their request to review the appointment of Juan Barros as bishop of Osorno.
Parishioners in the southern Chilean city say Bishop Barros used his position in the Church to try to block an investigation into the actions of his mentor, Catholic priest Fernando Karadima.
Activists fighting for the rights of sexual abuse victims has anyway gathered in Santiago for a conference.
They launched an organisation called Ending Clerical Abuse which “seeks to stop child sexual abuse by the clergy” worldwide.
One of the activists, Juan Carlos Cruz, told the BBC: “[Saying sorry] is not sufficient for a survivor. What we want is for the Pope to take action.”
Under Pope Francis, a Vatican committee has been set up to fight sexual abuse and help victims but Chilean victims of clerical sex abuse say more transparency is needed.