DUBLIN — Pope Francis said in an unprecedented letter to the world’s 1.2 billion Catholics on Monday that the church has not dealt properly with “crimes” against children and must prevent sexual abuses from being “covered up and perpetuated.”

“We showed no care for the little ones; we abandoned them,” Francis wrote.

The 2,000-word letter, the first by a pope addressed to the world’s Catholics on the topic of sexual abuse, amounted to a direct response by Francis to a rekindled crisis that has engulfed his papacy and eroded the credibility of the Catholic Church.

But after years of high-level pledges to end abuse, the letter renews questions about whether Francis will be able to follow through with a more concrete plan to overhaul the Vatican’s handling of sexual offenses.

His letter touched off mixed reactions from across the Catholic world, with some noting that Francis did not outline any specific new steps the church should take. But others said that Francis is coming to grips with the scale of the crisis and has increasingly described the problems as systemic or cultural, not simply the result of isolated priestly behavior.

“Looking ahead to the future, no effort must be spared to create a culture able to prevent such (abuses) from happening, but also to prevent the possibility of their being covered up and perpetuated,” Francis wrote.

The letter was issued at a time when revelations in the United States and around the world are roiling the church – and prompting new scrutiny over how the institution’s hierarchy handles abuse cases. A Pennsylvania grand-jury report released last week documented seven decades of abuse by 300 priests. It detailed cases of children who were allegedly raped, manipulated with alcohol and “brushed aside” by church leaders.

This weekend, Francis will travel to Ireland, a country scarred by decades of sexual abuse in parishes and in Catholic-run schools. In Dublin, many have demanded that Francis acknowledge during his trip the role church higher-ups played in silencing victims and helping to keep pedophile priests on the job.

While the Catholic Church has been dealing for more than three decades with publicly known cases of abuse, new cases in recent months have caused a wave of anger among Catholics, who say the Vatican has been slow to make meaningful reforms.

“The public, and Catholics in particular, are truly fed up with this. It’s beyond frustration,” said Peter Isely, a founding member of Ending Clergy Abuse, a global survivors and activists group. “They’ve had decades to do something. What it appears to look like is that nothing has significantly changed.”

Isely said that Francis is beginning to “correctly describe” the problem.

Popes have previously written letters on sexual abuse, but they were directed at individual countries – not at the broader Catholic world. In 2010, Pope Benedict XVI, in a letter to the Catholics of Ireland, told victims of abuse and their families that he was “truly sorry” and that the church in Ireland needed to acknowledge the “serious sins committed against defenseless children.”

Earlier this year, Francis sent a letter to the people of Chile describing a culture of “abuse and cover-up.” That move was particularly notable, coming just months after the pope, in a much-criticized move, had defended a Chilean bishop facing accusations of abuse.

“He has shown the capacity to change, and I think that’s the single most important lesson he has given us about himself,” said Jason Berry, a reporter and author who has covered sexual abuse for decades. “If he can evolve on this issue forcefully, he might have a chance at achieving some kind of genuine reform.”

Berry said that Francis’ letter was a first step – but that to go further he would have to contest a “calcified power structure that is honeycombed with secrecy.”

“He does not have a brain trust around him that is focused on systemic reform,” Berry said. “Right now they’re putting out fires.”

In his letter Monday, Francis specifically mentioned the Pennsylvania grand-jury report, but he did not reference other scandals in the United States, Chile or Australia. Francis said the Pennsylvania report reflected “abuse of power and of conscience.”

“The heart-wrenching pain of these victims, which cries out to heaven, was long ignored, kept quiet or silenced,” Francis wrote. “But their outcry was more powerful than all the measures meant to silence it, or sought even to resolve it by decisions that increased its gravity by falling into complicity.”

The U.S. church has also reeled from revelations about Cardinal Theodore McCarrick, the former archbishop of Washington, D.C., who resigned last month amid allegations that he abused seminarians and minors. McCarrick was able to climb the church’s hierarchy, becoming one of the U.S. church’s most powerful figures, even after two New Jersey dioceses paid out settlements in response to his alleged misconduct.

The McCarrick allegations, coupled with the report from Pennsylvania, have prompted American bishops to reckon with their failure to deal more forcefully with alleged abusers – whether they are priests or prelates.

One of the leaders whose actions have raised questions is Cardinal Donald Wuerl, the current archbishop of Washington, who during a previous posting in Pittsburgh disciplined some accused priests but reassigned others who were under scrutiny to new parishes, according to the grand-jury report.

Wuerl has defended his record and said the report shows that he acted “with diligence.” An Archdiocese of Washington spokeswoman said Wuerl has canceled a planned trip this week to Ireland, where he was scheduled to give a keynote speech at the World Meeting of Families.

Last week, Cardinal Daniel DiNardo, president of the U.S. Conference of Catholic Bishops, said the U.S. church should give a wider role to lay people in holding clerics accountable.

In his letter, Francis said he was aware of efforts in parts of the world to “come up with the necessary means to ensure the safety and protection of the integrity of children and of vulnerable adults, as well as implementing zero tolerance and ways of making all those who perpetrate or cover up these crimes accountable.”

“We have delayed in applying these actions and sanctions that are so necessary,” Francis wrote, “yet I am confident that they will help to guarantee a greater culture of care in the present and future.”

Francis also criticized the culture of clericalism – which some outsiders say creates a chasm of power between clerics and laity. Francis wrote that clericalism “helps to perpetuate many of the evils that we are condemning today.”

Kathleen Cummings, director of the Cushwa Center for the Study of American Catholicism at the University of Notre Dame, said Francis’ critique of clericalism gives her hope for reforms to come.

“He spoke about clericalism far more forcefully and explicitly in this letter,” she said.

More important, though, she said, is that church leaders welcome further investigations like the grand-jury report in Pennsylvania. The Catholic Church “should not be waiting for the attorney general to come knocking, but saying ‘Come in,’ ” Cummings said. “The only way to move past this crisis is to understand its magnitude.”