More than 1,000 children - and possibly many more - were molested by hundreds of Roman Catholic priests in six dioceses in the US state of Pennsylvania, while senior church officials took steps to cover it up, according to a landmark grand jury report released on Tuesday.

The grand jury said it believes the real number of abused children might be in the thousands since some records were lost and victims were afraid to come forward. The report said more than 300 clergy committed the abuse over a period decades, beginning in the mid-1950s.

Pennsylvania Attorney General Josh Shapiro said the two-year probe found a systematic cover-up by senior church officials in Pennsylvania and at the Vatican.

"The cover-up was sophisticated. And all the while, shockingly, church leadership kept records of the abuse and the cover-up. These documents, from the dioceses' own 'Secret Archives,' formed the backbone of this investigation," he said at a news conference in the city of Harrisburg.

The report faulted Cardinal Donald Wuerl, the former longtime bishop of Pittsburgh who now leads the Washington archdiocese, for what it said was his part in the concealment of clergy sexual abuse. Wuerl, one of the most prominent cardinals in the United States, released a statement Tuesday that said he had "acted with diligence, with concern for the victims and to prevent future acts of abuse".

The grand jury scrutinised abuse allegations in dioceses that minister to more than half the state's 3.2 million Catholics. Its report echoed the findings of many earlier church investigations around the country in its description of widespread sexual abuse by clergy and church officials' concealment of it.

Al Jazeera's Kristen Saloomey, reporting from Harrisburg, said the allegations made in the report were "really shocking".

Most of the abuse survivors were boys, but girls were abused too, the report said. The abuse ranged from groping and masturbation to anal, oral and vaginal rape.

"Church officials routinely and purposefully described the abuse as horseplay and wrestling ... It was none of those things. It was child sexual abuse, including rape," Shapiro said.

He also said that one priest had molested five sisters in one family. The diocese settled with the family after requiring a confidentiality agreement, according to Shapiro.

The attorney general said that Catholic bishops covered up child sexual abuse by priests and reassigned them repeatedly to different parishes. "They allowed priests to remain active for as long as 40 years," he said.

"Children were taught that this abuse was not only normal but that it was holy."

The panel concluded that a succession of Catholic bishops and other diocesan leaders tried to shield the church from bad publicity and financial liability by covering up abuse, failing to report accused clergy to police and discouraging victims from going to law enforcement. (BBC)

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