An investigation has been launched into the Swiss Bishops' Conference (SBC) following allegations of the mishandling of sexual abuse cases by several of its members.

Six bishops were accused of covering up abuse cases in a letter sent to the Apostolic Nuncio of Switzerland, Martin Krebs earlier this year. The Associated Press confirmed reports that Father Nicolas Betticher, a priest at the Bruder Klaus church in the Swiss capital Bern, had written the letter.

In a statement, Catholic bishops in Switzerland confirmed that some of the allegations also accuse some members of "having committed sexual assaults themselves in the past".

The claims against active and retired SBC members were made public on Sunday.

The Vatican ordered a preliminary canonical investigation into the matter in June following receipt of the letter from the President of the Bishops' Conference, Bishop Felix Gmür.

Bishop Joseph Bonnemain has been appointed to lead the inquiry, which is expected to be completed by the end of the year. According to the SBC's statement, Bonnemain has a history of investigating sexual assaults connected with the Church.

"The main subject of this preliminary church investigation is the allegations of covering up cases of abuse. The police and the public prosecutor's office are primarily responsible for investigating suspected sexual crimes," the SBC statement reads.

The body went on to explain that its guidelines "oblige church leaders to report suspected sexual offenses against minors - in consultation with the person concerned - to the public prosecutor's office". The SBC states that the relevant authorities were notified about the cases raised in the complaint.

"Since this is an ongoing case, we cannot provide any further information," it added.

The Catholic Church introduced a law in 2019, obliging clergy to immediately report any suspicions of cover-ups of sexual abuse cases with under-18s to the responsible bishop, who will escalate the concern to the Vatican.

Betticher's letter accuses six Catholic bishops of covering up cases of sexual abuse and a bishop and three priests of sexually abusing minors. Betticher claims he felt motivated to speak out following a call from Pope Francis for clergy members to report concerns about sexual abuse.

"Twenty years ago, we did not have a sufficient legal basis and therefore we made a lot of mistakes," Betticher told AP News. "Now, I see that for ten years, we have continued to make mistakes and today, there is a kind of will to hide certain things, or not to be precise, and not to go through with the checks (of allegations of sexual abuse)."

Betticher says the mishandling of such cases discredits the Church and needs to be addressed.

An independent study of abuse by Church authorities was approved by Swiss Catholic leaders in 2021 and is set to be released this week.