A nun has condemned the Catholic church’s hierarchy for its failure to tackle the scourge of clerical sexual abuse, saying leaders must concede that their “mediocrity, hypocrisy and complacency” has brought the church to a “disgraceful place”.

In her speech, delivered at the Vatican’s unprecedented summit on the issue, Sister Veronica Openibo from Nigeria said the church was in a state of “crisis and shame”.

“We proclaim the Ten Commandments and parade ourselves as being the custodians of moral standards, values and good behaviour in society,” she said. “Hypocrites at times? Yes. Why did we keep silent for so long?”

Openibo, one of only three women to address the event, went on to say the scandal had “seriously clouded the grace of the Christ mission”.

“Is it possible for us to move from fear of scandal to truth? How do we remove the masks that hide our sinful neglect?” she said.

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She said that while preparing her speech, she recalled the sadness felt after watching the Oscar-winning film Spotlight, which told the story of the Boston Globe journalists whose investigation exposed sexual abuse of minors by clergy and showed how most of the accused priests were simply moved to other parishes.

“How could the clerical church have kept silent, covering these atrocities?” she asked. “The silence, the carrying of the secrets in the hearts of the perpetrators, the length of the abuses and the constant transfers of perpetrators are unimaginable.”

Openibo, who has worked in Africa, Europe and the US, said: “Too often we want to keep silent until the storm has passed. This storm will not pass by. Our credibility is at stake.”

Opening the event on Thursday, Pope Francis said church leaders had a responsibility to deal effectively with the crimes of priests who rape and molest children and called for “efficient and concrete measures” to be established.

The pontiff and the 190 bishops and cardinals in attendance watched videotaped testimony from survivors of abuse telling of their trauma and the cruel indifference shown by church leaders.

One woman from Africa told the summit that a priest who had begun raping her at age 15 forced her to have three abortions, and beat her when she refused him sex. A survivor from Chile told the bishops and religious superiors they had inflicted even more pain on survivors by discrediting them and protecting priests who abused.

A list of 21 “reflection points” written by the pope is expected to provide the basis for the development of new anti-abuse procedures for bishops.

The summit will end on Sunday with a closing speech by the pope.