The Vatican on Tuesday denied a cover-up over a US ex-cardinal accused of sexual abuse, admitting mistakes were made but saying Theodore McCarrick's crimes had for years been nothing but rumours.

A 450-page report on who knew what -- and whether three consecutive popes overlooked McCarrick's abuse of at least one teenage boy and a number of male seminarians -- accused senior US clergy of providing "inaccurate and incomplete information to the Holy See" about his behaviour.

The influential former archbishop of Washington, DC, who played a key role in raising funds for the Holy See from wealthy US donors, was stripped of his cardinal's title in 2018 and his priest's status in 2019.

Now 90, he was found guilty by the Vatican of the abuse of teenager in the 1970s as well as years of misconduct -- such as inviting seminarians to his beach house where he made them share his bed.

He became the highest-ranking Church figure to be expelled in modern times.

The report, which comes with a graphic content warning and is based on documents as well as over 90 witness interviews, insists the first official allegation of paedophilia against McCarrick was not made until 2017 -- at which point the Vatican reacted.

US ex-cardinal Theodore McCarrick became the highest-ranking Church figure to be expelled in modern times
US ex-cardinal Theodore McCarrick became the highest-ranking Church figure to be expelled in modern times POOL / Jonathan Newton

The Catholic Church has been rocked by a global paedophilia scandal, with victims coming forward from countries including Australia, Chile and Germany as well as the United States.

The "often emotional" testimony from survivors in the McCarrick case revealed "sexual abuse or assault, unwanted sexual activity, intimate physical contact and the sharing of beds without physical touching", as well as detailed accounts of his abuse of power, the report said.

Survivors' groups have demanded to know how McCarrick -- who went by the nickname "Uncle Ted" -- was appointed to the prestigious Washington post in late 2000 and created cardinal in 2001, despite anonymous letters from the early 1990s accusing him of the carnal abuse of his "nephews".

Former Pope John Paul II had been advised it would be "imprudent" to promote McCarrick, but the latter wrote to the pontiff in 2000 insisting he had "never had sexual relations with any person, male or female, young or old, cleric or lay, nor have I ever abused another person".

His successor as pope, Benedict XVI, appears also to have been swayed by McCarrick swearing on his "oath as a bishop" that the allegations were false. The Vatican asked the cleric however to "maintain a low profile" -- a request he ignored.

Current Pope Francis, faced with the same rumours, "did not see the need to alter the approach that had been adopted in prior years", the report said -- until a concrete allegation of abuse against a minor was made in 2017.