Sex abuse scandals that have rocked the Catholic Church in the US have cost the institution almost $4 billion over six decades, the National Catholic Register (NCR) has found.

An extensive investigation revealed that the Church paid out at least $3,994,797,060 between 1950 and August 2015; almost $1bn more than previously estimated.

Changing methods of collecting and recording data, confidentiality restrictions and incomplete information mean that the figure is not final, and the NCR says it is "almost certainly a low estimate".

Scores of allegations of sex abuse by clergy have been made against the Catholic Church in recent years, and the Vatican admitted in 2014 that it had defrocked almost 850 priests in the past decade as a result.

In August, the Archdiocese of Milwaukee in Wisconsin became the latest in a number of archdioceses in the US to file for bankruptcy over sex abuse claims.

Pope Francis has denounced clerical abuse as "intolerable" and "the most terrible and unclean thing imaginable", and has met with survivors several times during his papacy.

Last year, he branded the crimes as similar to those of a "sacrilegious cult", asking "for the grace to weep, the grace for the Church to weep and make reparation for her sons and daughters who betrayed their mission, who abused innocent persons."

"Before God and his people I express my sorrow for the sins and grave crimes of clerical sexual abuse committed against you. And I humbly ask forgiveness," he added.

During his recent trip to the US, Francis highlighted the abuse of children in particular, and insisted that perpetrators of abuse would be held to account.

"I remain overwhelmed with shame that men entrusted with the tender care of children violated these little ones and caused grievous harm. I am profoundly sorry. God weeps," he told hundreds of thousands of people gathered for Mass in Philadelphia.

"The crimes and sins of the sexual abuse of children must no longer be held in secret. I pledge the zealous vigilance of the Church to protect children and the promise of accountability for all."