'Never again' says pope on abuse
'We will do everything possible,' pontiff vows11 June, 11:21
"We insistently ask for forgiveness from God and the persons involved," the pope told some 15,000 priests from all over the world at a Mass in St Peter's marking the end of the Year of the Priest.
The 83-year-old pontiff vowed to "do everything possible to make sure such abuse can never happen again".
Looking back on the Year of the Priest, the pope said that while being cause for celebration of the 'sacrament" of the priesthood it had coincided with the emergence of "sins of priests, especially towards children, in which the priestly role of helping humanity had been "turned around".
The pontiff vowed to weed out possible future predators when priests were selected and trained.
"We will do everything possible to weigh the authenticity of the (priest's) vocation," he promised.
"The Church "must use the shepherd's staff, the staff that protects faith against falsifiers, against leanings that are, in fact, distortions".
Alluding to cover-ups, he said "conduct unworthy of the priestly life cannot be tolerated".
The Catholic Church has this year been rocked by a series of sex abuse scandals and has had to fend off allegations that the Vatican covered up a number of cases.
Paedophile scandals have hit the Church in the United States, Australia, Ireland, Netherlands, Norway, Austria, Germany and Italy.
Benedict has repeatedly pledged to root out abuse but some victims groups have said they want to see "more concrete" steps.