LONDON — The Vatican is looking into allegations of inappropriate behavior by Cardinal Keith O’Brien, Britain’s most senior Catholic cleric, officials said Sunday.

The claims come at a sensitive time, as O’Brien and other cardinals prepare for a conclave to choose the next pope.

O’Brien, who heads the Roman Catholic Church in Scotland, was taking advice from lawyers after the British newspaper The Observer reported that three current priests and a former priest have filed complaints to the Vatican alleging that the cardinal approached them in an inappropriate manner.

The exact nature 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, was not spelled out. But one of the alleged victims claimed that O’Brien had started a “relationship” with him 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.

The paper didn’t cite the names of the priests, but it said their allegations date back to the 1980s. None of the four men could be independently reached.

“Cardinal O’Brien contests these claims and is taking legal advice,” said Peter Kearney, a spokesman for the Scottish Catholic Church.

The Vatican declined to confirm details of the allegations against O’Brien, saying only that Pope Benedict XVI had been informed of the “problem” Sunday and the matter was now “in the hands” of the outgoing pope.

In the coming weeks, O’Brien, 74, is expected to join a conclave of cardinals at the Vatican to elect the next pontiff, following Benedict’s resignation. O’Brien is due to retire when he turns 75 in March.

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.”

But in Britain, the Observer report was considered additionally explosive because of O’Brien’s public stance on homosexuality. Last year, O’Brien, who has described homosexuality as immoral, called the campaign to legalize same-sex marriage here a “grotesque subversion of a universally accepted human right.”

Allies of O’Brien, however, were quick to defend him, saying judgment should be reserved until a full airing of the facts emerged.

“These allegations have not been proved in any way,” Cardinal Cormac Murphy-O’Connor, former archbishop of Westminster, told the BBC.

– The Associated Press contributed to this report.