A former top Vatican official has accused Pope Francis of having known of allegations of sex abuse by a prominent U.S. cardinal for years and called on him to resign, in an unprecedented broadside against the pope by a Church insider.

In a detailed 11-page bombshell statement given to conservative Roman Catholic media outlets during the Pope's visit to Ireland, Archbishop Carlo Maria Vigano accused a long list of current and past Vatican and U.S. Church officials of covering up the case of Cardinal Theodore McCarrick, who resigned last month in disgrace.

In remarkably blunt language, Vigano said alleged cover-ups in the Church were making it look like "a conspiracy of silence not so dissimilar from the one that prevails in the mafia".

"Pope Francis has repeatedly asked for total transparency in the Church," wrote Vigano, who has criticized the pope before.

"In this extremely dramatic moment for the universal Church, he must acknowledge his mistakes and, in keeping with the proclaimed principle of zero tolerance, Pope Francis must be the first to set a good example for cardinals and bishops who covered up McCarrick's abuses and resign along with all of them," he said.

Vatican officials declined immediate comment on Sunday on the statement, which was published by the National Catholic Register and several other conservative media outlets in the United States and Italy.

Vigano said he had told Francis in June 2013, just after he was elected pope by his fellow cardinals, about the accusations against McCarrick.

Vigano, the papal envoy in Washington from 2011 to 2016, also said he had informed top Vatican officials as early as 2006 that McCarrick was suspected of abusing adult seminarians while he was a bishop in two New Jersey dioceses between 1981 and 2001. He said he never received a response to his 2006 memo.

He also accused McCarrick's successor as archbishop of Washington, Cardinal Donald Wuerl, of having been aware of the abuse allegations. Wuerl has said he did not know of them.

The statement was the latest blow to the credibility of the U.S. Church. Nearly two weeks ago, a grand jury in Pennsylvania released the findings of the largest-ever investigation of sex abuse in the U.S. Catholic Church, finding that 301 priests in the state had sexually abused minors over the past 70 years.