Cardinals attend a meeting at the Synod Hall in the Vatican (Reuters)

Cardinals from around the world have gathered in Vatican City for the first in a series of meetings leading to the election of a new pope.

The first general congregation of the College of Cardinals, the meeting preceding the conclave that is to identify a successor for Benedict XVI, was shaken by a phony bishop getting past security plus the repercussions of Cardinal Keith O'Brien's admission that he did behave "inappropriately" with young priests - a claim he had initially denied.

The 103 cardinals took the oath of secrecy to conceal all their delibarations in the run-up to finding a new pontiff.

At a press conference, Vatican spokesman father Federico Lombardi appeared visibly vexed by journalists' questions about the O'Brien scandal and the possibity of a Vatican inquiry being launched into the allegations of sexual misconduct.

"I don't have any specific information about this," Lombardi said. "What I can say is that the Pope had been informed.

"This briefing is about the conclave, we can't spend the morning taking about O'Brian. I have nothing else to say."

Phony Cardinal

Earlier, a fake bishop dodged Vatican security measures and sneaked into the pre-conclave meeting.

Wearing a suspiciously short cassock and a scarf instead of the purple episcopal sash, the imposter mingled with bishops and archbishops before he was kicked out.

"I know nothing about this," Lombardi said. "I haven't seen any fake bishop. I believe that those I saw were all true cardinals."

A further dozen cardinals are expected to join the congregation. Once convened, a starting date for the conclave will be set.

The first pope to resign in 600 years, Benedict stepped down because of old age and declining strength.

According to some Italian media reports, the real reason was that he had read a damning report by a commission of three cardinals on the Vatileaks scandal that revealed destructive power struggles and infighting in the Holy See.

Lombardi said the report would be handed only to the next pope and cardinals will not be briefed about it before the vote.

Julian Herranz, Josef Tomko and Salvatore de Giorgi - the cardinals who drew up the report - are taking part in the general congregation.