LISBON,  (Reuters) – Pope Benedict said yesterday  that the greatest threat to Catholicism came from “sin within  the Church”, one if his most forthright comments so far on a  sexual abuse scandal that has created turmoil in the church.  The Church has “a very deep need” to recognise that it must  do penitence for its sins and “accept purification”, he said.

“Today we see in a truly terrifying way that the greatest  persecution of the Church does not come from outside enemies but  is born of sin within the Church,” Benedict told reporters on  the plane to Portugal, replying to a question about the scandal.

In recent weeks, a number of Vatican officials have accused  the media, gays or progressives of waging a smear campaign  against the Church. One top Vatican official even dismissed  reports of a cover-up of sexual abuse of children by priests as  “petty gossip”.

The 83-year-old German pontiff, facing the worst crisis of  his five-year-old papacy, said the Church had to seek  forgiveness from victims of sexual abuse but also recognised  that “forgiveness cannot be a substitute for justice”.

The pope promised abuse victims he met in Malta last month  the Church would do all it could to investigate allegations,  bring to justice those responsible for abuse and implement  effective measures to protect young people in the future.

But the scandal shows no sign of abating. On Saturday Bishop  Walter Mixa of Augsburg, who has been accused of sexually  abusing minors, became the first bishop in the pope’s native  Germany to step down over the scandal. In recent weeks, a Belgian bishop resigned after admitting  he had sexually abused a boy and three Irish bishops quit over  their handling of sexual abuse cases.

In his comments on the plane, the pope also mentioned  Portugal’s economic crisis. The minority socialist government is  struggling to reduce a huge deficit but harsh austerity measures  will impose greater sacrifices to avoid a Greek-style debt  crisis.

Benedict, who was due to hold a large outdoor Mass yesterday afternoon, repeated his call for greater moral  responsibility in financial decisions and acknowledged the  Church should in the past have spoken out more on economics. “We must admit that the Catholic faith … was often too   individualistic. It too often left concrete things to the world  and thought only of individual salvation and religious affairs  without realising that there was a global responsibility (for  economic decisions),” he said.

The main purpose of the pope’s four-day visit to Portugal is  to visit the shrine at Fatima where the Madonna is said to have  appeared to three shepherd children six times in 1917.

One of the three messages the Madonna is said to have given  to the child visionaries — the so-called ‘Third Secret of  Fatima’ — was what the Vatican has said was a prediction of the  1981 assassination attempt against the late Pope John Paul.

Benedict told reporters he believed that interpretation of  the Third Secret, revealed in 2000, could include the suffering  the papacy and the Church would have to endure as a result of  today’s sexual abuse crisis.