Pope Benedict XVI has rebuked Irish bishops for "grave errors of judgement" in handling clerical sex abuse and ordered a Vatican investigation into the Irish church to wipe out the scourge.

There was no mention of any Vatican responsibility in the scandal and no specific punishments doled out for bishops blamed by victims and Irish government-ordered investigations for having covered up years of abuse.

In a pastoral letter to Irish faithful, Benedict said: "I am truly sorry" for the harm done to generations of Irish Catholics who suffered "sinful and criminal" abuse at the hands of priests, brothers and nuns.

"It is understandable that you find it hard to forgive or be reconciled with the church," he said. "In her name, I openly express the shame and remorse that we all feel."