Pope Francis begged for forgiveness in an unprecedented letter Monday and said Catholic leaders were to blame following a grand jury report last week that found more than 1,000 children were sexually abused by "predator priests" in Pennsylvania for decades.

"With shame and repentance, we acknowledge as an ecclesial community that we were not where we should have been, that we did not act in a timely manner, realizing the magnitude and the gravity of the damage done to so many lives," Francis wrote.

"We showed no care for the little ones; we abandoned them," he added.

The pope's 2,000-word letter addressed to the "People of God" came nearly a week after the damaging report was released detailing allegations of rampant sexual abuse in parishes across Pennsylvania.

Abuse complaints were kept in the church's so-called secret archive and church officials hid incidents, neglected to discipline priests or report them to law enforcement, according to the 1,356-page report.

"Priests were raping little boys and girls, and the men of God who were responsible for them not only did nothing; they hid it all," the report said.

The Vatican said in a statement two days after the report's release that the abuses described "are criminal and morally reprehensible" and "those acts were betrayals of trust that robbed survivors of their dignity and their faith."

The report was the result of a two-year investigation — the largest into sex abuse allegations within the U.S. Catholic Church — and had remained under seal during pending court challenges from clergy. The abuse dates to the 1940s and includes allegations against more than 300 priests, some of whom have since died.

Statute of limitations also prevents some of them from being criminally charged.

Francis said he supports "implementing zero tolerance and ways of making all those who perpetrate or cover up these crimes accountable."

The church has moved to defrock hundreds of priests in recent years after credible allegations of abuse have come to light.

In June, Cardinal Theodore McCarrick became one of the highest-ranking American clerics to be removed from public ministry because of sex abuse allegations.

The Vatican noted last week that the grand jury report found "almost no cases after 2002" of abuse — an indication that more recent reforms adopted by U.S. bishops may have helped to reduce cases of inappropriate clergy behavior.

As Francis looks to repair the church and help the world's 1.2 billion Catholics reconcile their faith with the latest abuse scandal, he is set to visit Ireland this weekend for the World Meeting of Families. Local reports say he may visit with abuse survivors in Ireland — a country similarly rocked by allegations against Catholic priests in the 1990s.

Francis on Monday said Catholic leaders who have failed to protect children must still be held accountable.

"It is essential that we, as a Church, be able to acknowledge and condemn, with sorrow and shame, the atrocities perpetrated by consecrated persons, clerics and all those entrusted with the mission of watching over and caring for those most vulnerable," he wrote. "Let us beg forgiveness for our own sins and the sins of others."