The 74-year-old cardinal, whose spokesman said contests the claims, was advised by lawyers to miss Sunday mass after complaints lodged two weeks ago with the pope's representative in Britain by a former priest and three currently serving priests from the cardinal's St. Andrews and Edinburgh Diocese were reported by The Observer.
The Independent of London reported a Vatican spokesman said the pontiff had been "informed about the problem and the question is now in his hands."
Bishop Stephen Robson said in a statement that the church "cannot not be saddened" by the allegations, The Independent said.
"The cardinal has sought legal advice and it would be inappropriate to comment at this time," he said.
The complaints allege inappropriate behavior dating back as far as 1980, The Observer said. The former priest said he was a 20-year-old seminarian at St. Andrew's College where O'Brien, his "spiritual director," approached him inappropriately after night prayers. Another priest said O'Brien initiated inappropriate contact during a visit to his parish. A third priest said he experienced unwanted behavior after a late-night drinking session when visiting O'Brien at the archbishop's residence and the fourth priest claims O'Brien used night prayers as an excuse for inappropriate contact.
The cardinal has a vote in the forthcoming papal conclave to choose Benedict's successor. The pope is stepping down at the end of the month.
The four accusers submitted their statements to the nuncio's office the week before Benedict announced his decision to resign. The Observer said the men fear if O'Brien takes part in the papal conclave, the church will not fully address their complaints.
"It tends to cover up and protect the system at all costs," one of them said. "The church is beautiful, but it has a dark side and that has to do with accountability. If the system is to be improved, maybe it needs to be dismantled a bit."
An outspoken opponent of gay rights, this past week O'Brien said the church should reconsider clerical celibacy.
O'Brien has, since 1985, been the archbishop of St. Andrews and Edinburgh.
Cardinal Cormac Murphy-O'Connor, the former archbishop of Westminster, said O'Brien himself will decide whether to attend the conclave in Rome.
"These allegations have not been proved in any way so I think he will have to decide whether he goes or not," Murphy-O'Connor said, adding that abuse allegations are now, in an age of transparency, "examined clearly and honestly and appropriate action is taken."
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