A former top Vatican official who dealt with clergy sexual abuse issues joined victims on Monday in urging Pope Francis to enact a zero-tolerance law throughout the global Catholic church so any cleric found guilty of abuse would be removed from ministry.

Rev. Hans Zollner, a German Jesuit priest who resigned in frustration from the pope's clergy abuse commission in 2022, was part of a press conference in Rome with Ending Clergy Abuse, an international group of victims.

They called on Francis to take a zero-tolerance law adopted by US Catholic bishops in 2002 and apply it to the entire 1.4-billion-member Church.

Zollner, who heads a centre for the study of abuse at Rome's Pontifical Gregorian University, said the Church needed "a change of knowledge, a change of attitude, a change of mentality (that is) much more than what has been done so far".

Francis has made addressing abuse by clergy a priority of his 11-year papacy, with mixed results so far.

In 2019, the pope mandated that all clerics report suspicion of abuse or cover-up to their church superiors. But he has not mandated reporting of abuse to civil authorities, except where required by local laws.

The US bishops enacted their zero-tolerance law with Vatican approval after extensive reporting on abuse scandals in Boston, where priests accused of sexual abuse had been moved from parish to parish for years.

The Vatican did not immediately respond to a request for comment about Monday's press conference. Vatican officials have in the past pointed to the difficulty of creating a single abuse reporting law for the hundreds of countries in which the Church operates.