In a long and highly unusual letter sent to US bishops as they embarked on a week-long retreat, Francis said the handling of the scandal showed the urgent need for a new approach to management and mindset within the Roman Catholic Church.

"God's faithful people and the Church's mission continue to suffer greatly as a result of abuses of power and conscience and sexual abuse, and the poor way that they were handled," the Pope wrote in Thursday's letter.

He added that bishops had "concentrated more on pointing fingers than on seeking paths of reconciliation".

Pope Francis has summoned the heads of some 110 national Catholic bishops' conferences and dozens of experts and leaders of religious orders to the Vatican on February 21-24 for an extraordinary gathering dedicated to the now global crisis.

Victims of clergy sexual abuse are hoping that the meeting will finally come up with a clear policy to make bishops themselves accountable for the mishandling of abuse cases.

Ahead of that encounter, US bishops gathered on Wednesday near Chicago for seven days of prayer and spiritual reflection.

"The Church's credibility has been seriously undercut and diminished by these sins and crimes, but even more by the efforts made to deny or conceal them," Francis said.

The Pope said he was so concerned by the situation that he had hoped to attend the retreat in person, but was unable to do so for "logistical reasons".

He sent his own preacher, Raniero Cantalamessa, to lead proceedings.

The US Church is still reeling from a grand jury report last year that found that 301 priests in the state of Pennsylvania had sexually abused minors over a 70-year period.

Australian Associated Press