Pope Francis has denied he knew about sexual misconduct by former US cardinal Theodore McCarrick before the start of Church investigations that found him guilty.

Mr McCarrick, once one of the most powerful men in the US Catholic Church hierarchy, was expelled from the priesthood in February after he was found guilty of sexual crimes against minors and adults.

"I knew nothing about McCarrick, naturally nothing," Pope Francis said in an interview with Mexico's Televisa broadcaster which has been published in Vatican media. "Otherwise, I would not have remained silent".

Last August, on the final day of Pope Francis' visit to Ireland, Archbishop Carlo Maria Vigano issued a statement accusing a long list of current and past Vatican and Church officials in the United States of covering up for McCarrick, 88, the former archbishop of Washington DC.

Archbishop Vigano, a former Vatican ambassador in Washington, said he told the pope shortly after his election in 2013 that McCarrick had preyed on adult seminarians for years.

Archbishop Vigano claimed that Pope Francis disregarded the information and effectively rehabilitated McCarrick, who had been quietly sanctioned by his predecessor as pontiff, the former Pope Benedict XVI, five years before the Argentinian's election in 2013.

Questioned by journalists on his flight from Dublin to Rome, Pope  Francis advised the media to examine the inconsistencies in Archbishop Vigano's account.

But he declined to comment on the substance of the allegations.

Now, nine months later, he has said he "does not remember" Mr Vigano ever telling him.

The interview with the pope was published on the same day that Monsignor Anthony Figueiredo, McCarrick's former secretary, posted a document on the internet with excerpts of emails and letters between him and McCarrick.

They showed that the Vatican never made the sanctions public and that high-ranking Vatican officials looked the other way as McCarrick openly flouted restrictions that had ordered him to keep a low profile.

Pope Francis celebrating mass at Phoniex Park during his visit last year

Mr Figueiredo's document was first reported by the Crux website and CBS.

McCarrick has said he has no recollection of abusing minors decades ago but has not commented publicly on the allegations of misconduct with adults by coercing them to share his bed, which was an open secret in the US church.

Pope Francis ordered a "thorough study" last year of all documents in Holy See offices concerning McCarrick and four US dioceses where he served have launched independent investigations.

In the excerpts of emails published by Monsignor Figueiredo, currently, a priest in Newark, New Jersey, McCarrick acknowledges "an unfortunate lack of judgment" with adult seminarians in their 20s and 30s but denies that there was any sex involved.

"I have never had sexual relations with anyone, man, woman or child, nor have I ever sought such acts," McCarrick said in a 2008 letter to a Vatican official.