Pope Francis has sent Catholic clergy a powerful reminder of their duty to stamp out sexual abuse of children by priests, warning that they must never let a fear of scandal lead to cover-ups.

In a strongly worded letter to the heads of national bishops’ conferences and religious orders, Francis demanded “close and complete” cooperation with a new child protection commission he has established at the Vatican.

The commission has been given a brief to drive reform on an issue that has severely damaged the church’s authority and reputation in many countries around the world.

Headed by the American cardinal Sean O’Mally, it includes both clerics and lay people, including two victims of paedophile priests, Marie Collins from Ireland and Peter Sanders from Britain. All 16 members, nine men and seven women, will meet for the first time in Rome on Friday.

“Families need to know that the church is making every effort to protect their children,” Francis wrote in the letter published on Thursday. “They should also know that they have every right to turn to the church with full confidence, for it is a safe and secure home.

“Consequently, priority must not be given to any other kind of concern, whatever its nature, such as the desire to avoid scandal, since there is absolutely no place in ministry for those who abuse minors.”

Francis’s letter follows the announcement last month that 10 priests and two Catholic lay workers in the Spanish city of Granada have been charged with the sexual abuse of altar boys between 2004 and 2007.

It is the biggest case of its kind in Spain, where the church has long been accused of exactly the kind of cover-up Francis was alluding to in his letter.