A former top Vatican official and critic of Pope Francis has accused the Pontiff of having known of allegations of sex abuse by a prominent US cardinal for five years before accepting his resignation last month, and he has called on him to resign.

In a detailed 11-page statement given to conservative Catholic media outlets during the Pope's visit here, Archbishop Carlo Maria Vigano also accused a long list of current and past Vatican officials and US Church officials of covering up the McCarrick case.

"Pope Francis has repeatedly asked for total transparency in the Church," wrote the former Papal Nuncio to the United States.

He has been critical of the 81-year-old Pope on previous occasions, such as on his decision to allow divorced and civilly remarried Catholics to receive Holy Communion under certain circumstances.

Pope will not say 'a single world' on cover-up claims

He has addressed public meetings alongside Cardinal Raymond Burke who, along with three other cardinals, have formally questioned five aspects of the Pope's 2016 teaching document 'The Joy of Love'.

However, Archbishop Vigano is also widely respected for blowing the whistle on financial corruption in the Vatican City state in 2011.

He was promptly moved by Pope Benedict XVI to a more senior job as Nuncio to the United States but is believed to have regarded the promotion as a way of frustrating his attempt to tackle financial corruption.

"In this extremely dramatic moment for the universal Church," Dr Vigano wrote, "he (Pope Francis) 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 Mr McCarrick's abuses and resign along with all of them."

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

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

Pope Francis began the mass in the Phoenix Park today by asking for forgiveness for the abuses of the Catholic Church in Ireland.

Dr Vigano, the papal ambassador in Washington from 2011 to 2016, said he had informed top Vatican officials as early as 2006 that Mr 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.

Mr McCarrick in July became the first Cardinal in living memory to resign his position in the Church leadership after a review concluded that claims he had sexually abused a 16-year-old boy were credible.

He was one of the highest-ranking church officials accused of sex abuse in a scandal that has rocked the faith since reports of priests abusing children and bishops covering up for them were reported in 2002.

Read more: Pope Francis in Ireland

Theodore McCarrick resigned in July

Since then patterns of widespread abuse of children have been reported across the United States and Europe, in Chile and Australia, undercutting the Church's moral authority and taking a toll on its membership and coffers

Mr McCarrick, 88, has said he had no recollection of alleged abuse of the minor but has not commented on widespread media reports that he would force adult men studying for the priesthood to sleep with him at a beach house in New Jersey.

Dr Vigano's statement railed against "homosexual networks present in the Church" - the word "homosexual" appears 18 times, while the word "child" appears only twice, in both cases in the titles of Church documents Dr Vigano sites.

Both today and yesterday, Pope Francis has asked for forgiveness for the "scandal and betrayal" felt by victims of sexual exploitation by Catholic clergy. 

Yesterday afternoon he said the corruption and cover-up of abuse amounted to human excrement, according to some of the eight victims he met in private for 90 minutes.

Additional reporting: Reuters