VATICAN CITY — Pope Francis was urged by a prominent church reform group Monday to oust the head of a powerful Vatican department after accusations that senior officials blocked reforms approved by the pontiff to curb sex abuse.

The row follows the resignation last week of Ms Marie Collins, an Irish survivor of clerical sex abuse, who stepped down from Francis's child protection panel slamming a "shameful" high-level obstruction of change in apparent defiance of the pope's wishes.

Cardinal Gerhard Mueller, head of the Congregation for the Doctrine of the Faith (CDF), replied Sunday to Ms Collins's claim that his department had ignored Francis's decision in 2015 to create a new tribunal to judge bishops who cover up sexual abuse cases.

In an interview with Italy's Corriere della Sera daily, he said the tribunal was merely a "project" which Vatican departments felt would needlessly duplicate initiatives already in place to deal with wayward bishops.

An international group called We Are Church issued a statement urging Pope Francis to replace Mr Mueller "with someone who will introduce transparency, justice and compassion" in the CDF.

It accused the department of refusing to set up the tribunal in question and refusing to "change the processes it uses for investigating priests".

"The CDF has come to symbolise those aspects of our church that serve to protect and preserve institutional power," said Ms Sigrid Grabmeier, the reform group's chair.

"For the good of our church, substantive change -- a conversion, really -- is needed in this important office. And quickly," she added.

Since his election in 2013, Pope Francis has repeatedly promised to root out abusers, once describing their actions as comparable to participating in a Satanic mass.

He has also attempted to end a cover-up culture. But critics say his good intentions are proving little more than that.

In his most recent comment on the issue, in a December letter to bishops, Pope Francis called for a renewed commitment to "zero tolerance," implicitly acknowledging much remains to be done. AFP