Pope Benedict XVI has spoken from Rome to apologise to victims of child sex abuse by Irish clergy.

The pope, in a letter addressing the abuse of minors in Ireland, announced a formal probe at religious institutions in the country, where he said children has suffered "grievously."

In the letter, the Pope also announced a full Vatican investigation of Irish dioceses, seminaries and religious orders, which had been affected by the scandal.

He said he was "truly sorry" and was willing to meet victims to acknowledge their suffering personally.

Pope Benedict warned that priests and religious workers guilty of child abuse should answer for their crimes, saying Irish bishops had made "serious mistakes" in responding to allegations.

Buts some Irish victims of clerical child sex abuse have said they are deeply disappointed by the Pope's letter of apology, saying it is narrowly focused on lower-rank Irish priests without recognising the responsibility of the Vatican and senior Irish clerics.

There have been five official Irish government reports over the past five years revealing ill-treatment, abuse and cruelty by clerics in the Catholic Church and cover-ups by religious authorities.

New Catholic Church abuse scandals have recently come to light in Germany, Austria, the Netherlands and Switzerland.