Former Pope Benedict has blamed the Catholic Church’s sexual abuse scandal on the effects of the sexual revolution of the 1960s.

The 91-year-old said a move away from absolute views of right and wrong towards a world where 'there could only be relative moral judgments' has caused a general collapse in morality that had also infected the priesthood.

He also bemoaned the fact that seminaries had an openly gay culture and thus failed to train priests properly.

As a solution, he proposes a return to Catholicism's absolute moral standards while also reforming church law to give more emphasis to protecting the faithful.

Former Pope Benedict has blamed the Catholic Church's sex abuse scandal on a decline of moral values that started with the sexual revolution of the 1960s

Benedict, who became the first Pope to resign in 2013, spoke out in a rare 6,000-word letter penned in his native German.

He said he felt compelled to write the note after Pope Francis invited the world's bishops to attend a conference at the Vatican to address the sex abuse crisis.

While he says that he is 'no longer directly responsible' for the Vatican's affairs, he wanted to help contribute to a 'new beginning' within the church.

He contacted Francis ahead of publishing the letter, he said, though did not say whether the Pope had responded.

The letter emerged as the Catholic Church in Japan said it was preparing to investigate allegations of sexual abuse against minors by its priests.

Benedict recommends a return to the church's strict moral codes as well as redrafting church laws 'to protect the faithful' as a way out of the crisis

The Catholic Bishops’ Conference in Japan said Thursday it has established a committee per district to investigate claims, some of which date back 20 years.

Surveys had found two reported cases in 2002 and five in 2015 which weren’t disclosed or verified, the conference said. They will be retroactively investigated.

Francis has been under pressure to act over sex scandals that have engulfed churches around the world.

In perhaps the highest profile case, Cardinal George Pell - the Vatican's third in command - was jailed for six years for molesting two teenage choirboys in the 1990s.

The former Vatican treasurer, 77, and top adviser to Pope Francis, is the most senior Catholic figure ever to be found guilty of sex offences against children.