saying he would not utter "a single word" about the accusations and suggesting, rather, that journalists read the statement and draw their own conclusions from the report.
"When some time passes and you have drawn your conclusions, I may speak".
The Pontiff accepted McCarrick's resignation as cardinal last month, after a USA church investigation determined that an accusation he had sexually abused a minor was credible.
Archbishop Carlo Maria Vigano, a former Vatican envoy to the United States, said he had told Francis of the allegations against prominent USA cardinal Theodore McCarrick in 2013.
He said the pope "knew from at least June 23, 2013, that McCarrick was a serial predator", adding that "he knew that he was a corrupt man, he covered for him to the bitter end".
His letter identifies by name the Vatican cardinals and USA archbishops who were informed about the McCarrick affair, an unthinkable expose for a Vatican diplomat to make. He does not offer any proof for his statements.
He served as the Vatican's ambassador to Washington from 2011 until 2016. "He must honestly state when he first learned about the crimes committed by McCarrick, who abused his authority with seminarians and priests".
In July, the pontiff accepted the resignation of McCarrick, now 88.
Pope Francis said on Sunday he would not respond to a former top Vatican official who accused him of having known for years of allegations of sex abuse by a prominent USA cardinal, calling on the pontiff to resign in an unprecedented broadside against the pope by a Church insider.
Despite the overwhelming emphasis on abuse, the Pope told reporters on his flight back to Rome that he "found so much faith in Ireland".
On each occasion he asked for forgiveness, the congregation - estimated by the Vatican to number 300,000 - applauded.
Years of sexual abuse scandals have shattered the credibility of the church, which dominated Irish society four decades ago.
Among them were protesters of the Catholic Church. While organisers predicted 500,000 would attend Francis' Mass, estimates put it the attendance figure at just 200,000.
The Tuam home was one of 10 institutions to which about 35,000 unmarried pregnant women are thought to have been sent.
Pope Francis returned to the Vatican last night after two days spent in Ireland.