Pope Francis has angered people who suffered sexual abuse by the clergy by praising American bishops for their "generous commitment" to helping victims.

Advocates hit back, saying the bishops acted only under the threat of hundreds of lawsuits.

Addressing church leaders in a prayer service at Washington cathedral, Francis said they had faced the crisis "without fear of self-criticism and at the cost of mortification and great sacrifice".

"I realise how much the pain of recent years has weighed upon you and I have supported your generous commitment to bring healing to victims - in the knowledge that in healing we, too, are healed - and to work to ensure that such crimes will never be repeated," the Pope said to loud applause from the bishops.

But the Survivors Network of Those Abused by Priests said the bishops had displayed "cowardice and callousness" in response to victims who came forward and they "hide behind expensive lawyers and public relations professionals" instead of fully confronting the scope of the problem within the church.

Anne Barrett Doyle, co-director of BishopAccountability.org, an advocacy group that collects records on abusive priests from around the world, called the Pope's remarks "distressing and quite off-base".

Vatican spokesman the Rev Federico Lombardi defended Francis' comments, saying it was appropriate to recognise the bishops' reforms in response to the scandal given the US church is now a model for other countries to follow.

"I am not surprised there are critics that are not happy, but this is not the first time," he said.

He said the Pope cannot simply keep beating down the bishops but must offer them words of encouragement.

The abuse crisis erupted in 2002 with the case of one pedophile priest in the Archdiocese of Boston, then spread nationwide. The revelations in Boston, about guilty priests kept in ministry without any warning to parents or police, persuaded thousands of people across the country to come forward with abuse claims, prompted grand jury investigations in several states and compelled the bishops to take an inventory of how every American diocese had dealt with perpetrators and victims going back decades.