Pope Francis criticised the mayor of Rome during an in-flight press conference on the way home from America, according to Italian media reports.
The Pontiff reportedly referred Mayor Ignazio Marino as someone who “professes to be Catholic”.
Speaking on the flight home to Rome, Francis was asked whether he had invited the mayor, a supporter of same-sex marriage and euthanasia, to join him in Philadelphia.
He is reported to have replied: “I didn’t invite the mayor. Is that clear? I asked the organisers and they didn’t invite him either.”
The Holy Father reportedly added that “He professes to be Catholic, it came on him all of a sudden. It doesn’t happen like that.”
Mr Marino is unpopular in Italy and his presence on the final part of the papal visit, which followed a holiday in the Caribbean, was criticised at home.
The apparent tension between the Pope and mayor is especially problematic in light of the upcoming Holy Year of Mercy in December, which the Vatican reportedly fears Rome is ill-prepared for.
The Italian media leaped on the Pope’s comments, with La Stampa commenting that “If the most popular man in the world takes down one of the least popular in Italy, that says that all the rules of the game have been thrown up in the air, including possibly those of mercy.”
Some 20 million pilgrims are expected for the Year of Mercy, which begins on December 8.