LONDON — On the same day as his last public blessing Sunday, Pope Benedict XVI confronted the threat of a fresh scandal within the church hierarchy, with Vatican officials informing him of new allegations that Britain’s most senior Roman Catholic cleric had engaged in inappropriate behavior with priests.
In Britain, the accusations against Cardinal Keith O’Brien, head of the church in Scotland and one of this nation’s most strident opponents of gay rights, were already escalating into a national furor.
The controversy revolved around a report first published Saturday night on the website of Britain’s Observer newspaper, saying that four men — three current priests and one former priest — had denounced O’Brien for ‘‘inappropriate’’ and ‘‘intimate’’ behavior.
Through a spokesman, O’Brien denied the charges and said he was seeking legal counsel.
A Vatican spokesman, the Rev. Federico Lombardi, said Sunday that the Vatican would investigate the complaints, which had been channeled through the office of the papal nuncio — the Vatican’s ambassador — in London.
‘‘The pope has been informed, and the question is in his hands,’’ Lombardi said.
If proven true, the allegations could rock the church at a highly sensitive time, highlighting a Vatican in crisis as its cardinals begin to gather in Rome to pick the pope’s successor after his surprise resignation earlier this month.
The exact nature and timing of the alleged contact, which the Observer said was reported to the Vatican’s emissary in London a week before Benedict’s Feb. 11 resignation, were not spelled out.
But one of the accusers said O’Brien had started a ‘‘relationship’’ with him in the 1980s that resulted in the need for long-term counseling. Another of the men said O’Brien had initiated ‘‘inappropriate contact’’ during nightly prayers, according to the paper.
Poised to join the upcoming conclave to elect a new pope, O’Brien missed Sunday Mass in his dioceses of St. Andrews and Edinburgh.
His auxiliary, Bishop Stephen Robson, read a statement at the cathedral in Edinburgh, saying: ‘‘A number of allegations of inappropriate behavior have been made against the cardinal. The cardinal has sought legal advice and it would be inappropriate to comment at this time. There will be further statements in due course.’’ He added, according to the BBC, ‘‘It is to the Lord that we turn to now in times of need.’’
The Vatican declined to confirm details of the allegations against the 74-year-old O’Brien, who was due to retire next month, saying only that Benedict had been informed.
The pope, who will step down Thursday evening, gave his final Sunday blessing from his studio window to the cheers of tens of thousands of people packing St. Peter’s Square, but sought to reassure the faithful that he wasn’t abandoning the church by retiring to spend his final years in prayer.
While the 85-year-old pontiff has lately looked tired and frail, the crowd filling the cobblestone square seemed to energize him, and he spoke in a strong voice, repeatedly thanking the faithful for their closeness and affection.
Benedict told the crowd that God is calling him to dedicate himself ‘‘even more to prayer and meditation,’’ which he will do in a monastery being renovated for him in Vatican City.
‘‘But this doesn’t mean abandoning the church,’’ the pope said. “I can continue to serve it with the same dedication and the same love which I have tried to do so until now, but in a way more suitable to my age and to my strength.’’
The allegations against O’Brien surfaced a week after the church became the focus of fresh leaks in the Italian press, which cited an internal Vatican report as detailing the existence of a gay lobby inside the institution that was subject to outside blackmail.
Responding to the reports, the Vatican’s Secretariat of State chided the media for ‘‘widespread distribution of often unverified, unverifiable, or completely false news stories that cause serious damage to persons and institutions.’’
In Britain, however, the Observer report was considered additionally explosive because of O’Brien’s public stance on homosexuality. Last year, O’Brien decried the campaign to legalize same-sex marriage here as a ‘‘grotesque subversion of a universally accepted human right.’’
He has described homosexuality as immoral and was singled out by the gay advocacy group Stonewall for a 2012 ‘‘bigot of the year’’ award.
Allies of O’Brien, however, were quick to defend him, saying judgment should be reserved until a full airing of the facts. ‘‘These allegations have not been proved in any way,’’ Cardinal Cormac Murphy-O’Connor, former archbishop of Westminster, said. ‘‘So I think he will have to decide whether he goes or not’’ to the conclave. ‘‘We must listen first of all to what he has to say.’’
The Observer’s report did not specify the extent to which the alleged encounters were consensual or ultimately resulted in sexual acts. None of the four men were named, and they could not be independently reached.
The paper said the men recently reported their claims to the Vatican emissary in London with the aid of an intermediary from their diocese in the week before the pope’s resignation.
The move appeared pegged to O’Brien’s planned retirement next month. The men were demanding O’Brien’s immediate resignation and apparently went public in an effort to block the cardinal from taking part of the papal conclave.