A former Vatican diplomat who accused the Pope of covering up reports of clerical sex abuse is lying low over fears for his safety, it is claimed.
Archbishop Carlo Maria Vigano wrote in a letter that Pope Francis knew of allegations against a US cardinal five years before accepting his resignation.
Italian blogger Aldo Maria Valli later said the archbishop had told him that he had "purchased an aeroplane ticket".
The senior priest has made no further comment since the weekend.
Recounting a meeting between the pair, Valli describes what the archbishop told him, writing: "He will leave the country. He cannot tell me where he is going. I am not to look for him. His old mobile phone number will no longer work. We say goodbye for the last time."
Similar claims that the archbishop is concerned about his safety were made by Edward Pentin of the conservative National Catholic Register.
Journalist Marco Tosatti, who says he helped the archbishop draft his bombshell 11-page letter, which was published on Sunday, told the BBC: "I don't know where he may be. He told me that he wanted to remain quiet. And at the moment, he's not answering his phone."
He made no mention of threats to his welfare, however.
What did the Archbishop's letter say?
In his letter, Archbishop Vigano said he told Pope Francis that Cardinal Theodore McCarrick, the former archbishop of Washington, had been accused of sexually abusing lower-ranking seminarians and priests over decades.
He said Pope Francis' predecessor, Pope Benedict XVI, had taken action against the cardinal, forcing him to withdraw to a life of "prayer and penance".
However, he said Francis had lifted the sanctions against him and allowed him to return to full duties.
Pope Francis "knew from at least 23 June 2013 that McCarrick was a serial predator", the archbishop wrote, adding: "He knew that he was a corrupt man, he covered for him to the bitter end."
"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," Archbishop Vigano wrote.
The archbishop, who served as the Vatican's envoy in Washington from 2011 until 2016, has produced no evidence of his alleged 2013 conversation with the Pope.
How has the Pope reacted?
Pope Francis has declined to comment on the claims against him.
"I will not say a word about that. I think the statement speaks for itself," he told journalists on his plane as he flew back to Rome on Monday.
The Pope urged those present to "read the document carefully and judge it for yourselves".
"You have sufficient journalistic capacity to draw conclusions," he added.
How have Catholics responded?
Reaction from within the Catholic community has varied widely, reflecting divided attitudes to Pope Francis.
While more progressive Catholics have praised the Pope's engagement with social issues, the church's conservative wing regard him as unsuitably liberal.
Some Catholics have called for a full investigation into Archbishop Vigano's allegations.
Others have pointed to perceived inconsistencies - including the fact that Cardinal McCarrick was seen in public with Pope Benedict after the date he was supposedly sanctioned by him.
Nicolas Seneze, the Rome correspondent for the French daily La Croix, told the AFP news agency there is "a clear desire to attack" the pontiff.