Pope Francis has dismissed the church's chief of doctrine, Cardinal Gerhard Muller - one of the most powerful cardinals at the Vatican - head of the Vatican office that processes and evaluates all cases of priests accused of raping or molesting minors.

Mueller's sacking on Saturday comes just days after the pontiff released another top Vatican cardinal, Cardinal George Pell, to return home to stand trial for alleged sexual assault.

"There were no differences of opinion between me and Pope Francis," Muller, an arch-conservative who had the ear of former Pontiff Benedict XVI, told the German paper Allgemeine Zeitung.

Francis named Muller's deputy, Monsignor Luis Ladaria Ferrer, a Spanish Jesuit, to run the powerful office instead.

During Muller's five-year term, the congregation amassed a 2,000-case backlog and came under criticism from Irish abuse survivor Marie Collins.

She had been tapped by Francis in 2014 to advise the church on caring for abuse victims and protecting children from paedophile priests.

Collins resigned from the papal commission in March, citing the "unacceptable" level of resistance from Muller's office to heeding the commission's proposals.

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In May, Francis said her criticism of the slow pace in processing abuse cases was justified and announced he was adding more staff to handle the load.

Earlier this year, he also named Cardinal Sean O'Malley as a member of the congregation in hopes of ensuring better cooperation.

Spar over divorce

Aside from the sex abuse case backlog, Francis and Muller had sparred over the pope's divisive 2016 document on family life in which the pope offered a cautious opening to letting divorced and civilly remarried Catholics receive Communion.

Church teaching holds that unless these Catholics receive an annulment, or a church decree that their first marriage was invalid, they are committing adultery and cannot receive Communion unless they abstain from sex.

Four conservative cardinals attacked the pope's document as vague and confusing and publicly requested that Francis clarify it.

Muller did not join their campaign but made it clear that he disagrees with Francis' suggestion that any such decisions could be arrived at in the realm of personal discernment.