Pope Benedict XVI yesterday rebuked Irish bishops for the negligent way they have handled sexual abuse cases in the Catholic church and issued an unprecedented public apology to the victims of paeodophile priests.

"You have suffered grievously and I am truly sorry," Benedict wrote in a pastoral letter released yesterday, which will be read at Catholic masses in Ireland. The letter also announced the setting up of a Vatican investigation team. "Many of you found that, when you were courageous enough to speak of what happened to you, no one would listen," he added. He accused bishops in Ireland of "grave errors of judgment" in their handling of thousands of "sinful and criminal" cases of abuse spread over decades.

Split into sections, the letter addresses victims, Irish bishops, abusive priests and parents. "There has never been a letter like this," said the pope's spokesman, Father Federico Lombardi.

The letter does not admit any responsibility on the part of the Vatican in relation to the scandals, nor does it specify punishments for Irish bishops who covered up for paedophile priests, moving them from parish to parish.

Following revelations that he swore abuse victims to secrecy in 1975, Cardinal Seán Brady, the head of the Irish Catholic church, has said he will seek guidance through prayer before deciding on his future. Benedict has yet to accept the resignations offered by three Irish bishops. Following the release of the letter, Brady said that all Irish Catholics should reflect upon it. "I welcome this letter," he said. "I am deeply grateful to the holy father for his profound kindness and concern."

It is evident from the pastoral letter that Benedict is deeply dismayed by what he refers to as "sinful and criminal acts and the way the church authorities in Ireland dealt with them".

Lombardi said yesterday there were no pointers to be found on Brady's future in the letter, which did not have an administrative or disciplinary function. "This is a pastoral letter... That is not touched on here," he said.

The letter comes as a new tide of sex abuse allegations threatens to engulf the Catholic church. Benedict himself has come under pressure over the explosion of abuse revelations in his home country, Germany, following a wave of cases in the US. Maeve Lewis, the Irish director for the campaign group against child abuse, One in Four, said she was "deeply disappointed" by the letter. "It falls short of what victims want, since it only tackles failures in the Irish church and not the failures that go right to the top of the Vatican, such as the 2001 ruling on secrecy," she said. "The church is still in denial."

Reports on abuse commissioned in Ireland have singled out a letter written by the current pope, then Cardinal Ratzinger, in 2001 instructing bishops to report all abuse cases to his office at the Vatican's Congregation for the Doctrine of the Faith for confidential handling. Vatican officials have said the measure was designed to prevent cases being covered up at local level, but Irish bishops reportedly understood the letter to mean they should not report cases to the police. In yesterday's letter, Benedict urged Ireland's bishops to "continue to co-operate with civil authorities".

"That could be interpreted as an instruction on mandatory reporting of abuse to the police, and this is welcome, although it is not clearly stated," said Lewis. "But where the pope goes on to deal with the proper application of canon law in these cases, it suggests he has no idea that civil law supersedes canon law, that bishops should abide by civil law like any citizen."

The letter announces that a Vatican investigation, or apostolic visitation, will be carried out at a "certain diocese" in Ireland, as well as in seminaries and religious congregations. Such investigations are carried out when the Vatican believes a local church is unable to put its own house in order.

"A lot of people will be quaking in their boots in Ireland as they wait to see which diocese the pope means," said one church insider in Ireland.

But Benedict also sympathised with Irish bishops, telling them: "I recognise how difficult it was to grasp the extent and complexity of the problem, to obtain reliable information and to make the right decisions in the light of conflicting expert advice."

Rather than blaming abuse on an oppressive, conservative environment within the Irish Catholic church, Benedict singles out the creeping influence of liberal, secular society for weakening resolve against it. "In particular, there was a well-intentioned but misguided tendency to avoid penal approaches to canonically irregular situations," he writes.

Lewis added: "We are astounded that the pope links the problem to secularisation. It shows a misunderstanding of the dynamics of sexual violence and suggests there is little hope the church will ever know how to respond."