Pope Francis has written an unprecedented letter to all the world's Catholics promising that no effort will be spared to prevent clerical sex abuse and its cover-up.

In the 2,000-word letter the pope condemns abuse, addresses previous failures to deal with the issue and begs for forgiveness for his own sins in relation to the handling of abuse.

Addressed to "the people of God", the pope appeared to be launching an appeal for all Catholics to face the sexual abuse crisis together and not let it tear the Catholic Church apart.

"We have realised that these wounds never disappear and that they require us forcefully to condemn these atrocities and join forces in uprooting this culture of death," he said.

The pope also responded to a recent grand jury report in the US state of Pennsylvania.

He said that while most cases in the report "belong to the past", it was clear that abuse "was long ignored, kept quiet or silenced".

Quoting a Gospel passage that says "If one member suffers, all suffer together," Pope Francis added: "(Those words) forcefully echo in my heart as I acknowledge once more the suffering endured by many minors due to sexual abuse, the abuse of power and the abuse of conscience perpetrated by a significant number of clerics and consecrated persons.

"With shame and repentance, we acknowledge as an ecclesial community that we were not where we should have been, that we did not act in a timely manner, realising the magnitude and the gravity of the damage done to so many lives.

"We showed no care for the little ones; we abandoned them."

A Vatican official said it was the first time a pope had written to all of the world's 1.2 billion Catholics about sexual abuse.

Past letters on the scandal have been addressed to bishops and faithful in individual countries.

The grand jury last week released the findings of the largest-ever investigation of sex abuse in the US Catholic Church, finding that 301 priests in the state had sexually abused minors over the past 70 years.

The letter was released as the church is facing sexual abuse scandals in a number of countries, including Chile and Australia.

It also comes just days ahead of the pope's two-day visit to Ireland for the conclusion of the World Meeting of Families.

There have been calls by victims' groups for Pope Francis to address the issue of abuse within the church in Ireland during his visit.

A leading victims’ advocate has responded to the Pope's statement by calling for urgent reform of the church's internal or canon law.

BishopAccountability.org, a US-based resource centre that tracks cases of clerical abuse worldwide, said that if Pope Francis wants to stop the abuse of children, he could make zero-tolerance universal canon law.

Speaking at a press conference in Dublin ahead of the World Meeting of Families this weekend, Anne-Barrett Doyle said: "Zero-tolerance does exist for US bishops - that is the only national abuse conference in the world, for which the Vatican has recognised zero-tolerance.

"That’s defined as when a priest abuses even one child under a canonical process - if his guilt is recognised or he admits it - he is removed permanently from ministry."

Yesterday, the Catholic Archbishop of Dublin Diarmuid Martin said it was not enough for the church to simply apologise for the abuse scandals.

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Meanwhile, former president Mary McAleese believes the Catholic Church is at a "tipping point".

Speaking at Trinity College Dublin, she said that whatever happens next will dictate whether it has a "healthy future or collapses in on itself".

She also expressed hope that the church will change its teachings on homosexuality.

However, the former president admitted that she "doesn't know" if it will.

Asked about the Pope's letter to Catholics, Mrs McAleese said she had not read it in full and was hesitant to comment until she had.

Read more: The Pope in Ireland