The Vatican has revealed that 400 priests were defrocked during two years of the pontificate of now pope emeritus Benedict XVI for child sex abuse crimes.

Vatican spokesman Federico Lombardi said: "In 2012 there were around 100, while in 2011 there were around 300. Some were as a result of a disciplinary procedures, others made a request," 

Scores more were defrocked in the preceding years, after Benedict XVI, the Vatican's former chief doctrine enforcer, was elected in 2005 to replace John Paul II.

But the Survivors Network of those Abused by Priests (SNAP) said these disciplinary measures were not enough.

"The pope must start defrocking clerics who cover up sex crimes, not just clerics who commit them. Until that happens, little will change," the US-based victim support and campaign group said in a statement.

"Defrocking is more defence strategy than child protection," it said, adding that the increase was likely due to the fact that more victims "are gaining the strength and courage to come forward" SNAP added.

Starting in Ireland and the US more than a decade ago, revelations of sex crimes by clergy and subsequent cover-ups by their bishops began emerging around the world and rocked the Roman Catholic Church.

Benedict XVI, who resigned last year and was replaced by Pope Francis, vowed zero tolerance for offending priests and the Vatican has reported receiving thousands of reports of abuse from local dioceses.

The Vatican's doctrinal watchdog, the Congregation for the Doctrine of the Faith, which investigates abuses under Canon Law, does not usually make its work public.

It says this is done for the protection of victims and witnesses, although victim support groups say it shows a continuing lack of transparency on the issue.

A Vatican delegation earlier this week was pushed for the first time to provide answers to the United Nations over its commitment to stamp out abuse by priests in front of the UN's child rights committee in Geneva.

"The Holy See gets it, that certain things have to be done differently," Charles Scicluna, the Vatican's former top prosecutor for sex crimes, told the meeting.

Pope Francis last Thursday said the scandals were "the shame of the Church" and has set up a committee to investigate claims and offer care for victims.

Campaigners say not enough is being done to cooperate with local police and judiciary, even though many claims have expired under statutes of limitations.

"Catholic officials should help make sure child molesting clerics are criminally prosecuted," SNAP said.

There are around 400,000 Catholic priests in the world.