Catholic cardinals on Thursday put off a decision on when to begin a conclave to elect the next pope, instead debating Vatican finances and a reform of its intrigue-filled bureaucracy in discussions held under an oath of secrecy.

Vatican spokesman Federico Lombardi said the last of the 115 "cardinal electors" who will take part in the vote, Vietnam's Jean-Baptiste Pham Minh Man, had arrived in Rome and taken his oath.

Only cardinals aged under 80 can participate and there had been several late arrivals after Benedict XVI's sudden decision to step down as leader of the world's 1.2 billion Catholics.

"There has been no decision on a date for the conclave," Lombardi said in a statement.

Earlier Thursday, three top Vatican officials in charge of economic affairs had reported to the cardinals in closed-door talks where all the participants are bound not to reveal any details.

Lombardi said he could not say whether or not there had been talk about the Vatican bank, which has been investigated in Italy for failing to comply with anti money laundering legislation.

Popular Italian Catholic weekly Famiglia Cristiana meanwhile said the Church was "losing credibility" over its finances and called for the Vatican bank to be replaced by "ethical banks".

Cardinals have been holding a series of meetings and prayers known as "general congregations" in the Vatican this week, identifying key problems for the Church that the new pope will have to face after Benedict's often troubled eight-year reign.

At the last "general congregations" in 2005, cardinals took just three days to set a date for the conclave and the delay this time around is being seen as a reflection of the many challenges facing the Church.

"There are no definite voting blocs or strong candidates. The situation is changing quickly," said Marco Politi, a Vatican expert who writes for the Italian daily Il Fatto Quotidiano.

"There is a lot of confusion," he said.

Vatican intrigue and the ongoing scandal over paedophile priests and the cover-up of their crimes have rocked the Catholic Church, where divisions between reformers and traditionalists have also appeared over key issues like priestly celibacy, female priests and contraception.

Vatican staff meanwhile continued preparing the famously frescoed Sistine Chapel for the momentous event, even installing the two stoves that will produce white smoke from burnt ballots once a cardinals wins a two-thirds majority.

The 85-year-old Benedict XVI last month became the first pontiff to resign since the Middle Ages, saying he lacked the strength of body and mind to carry on in a fast-changing modern world.

US cardinals had raised the issue of reform of the Curia in daily media briefings that were abruptly stopped on Wednesday for fear of "leaks" after Italian media reported that "sparks" were flying between American and Italian cardinals.

There was more fuel for the fire on Thursday after Italian daily La Repubblica published an interview with an anonymous Vatican source who said whistleblowers in the Holy See administration wanted to expose corruption.

Benedict's butler Paolo Gabriele was convicted last year for leaking hundreds of confidential papal papers in an apparent effort to help the pope clean up the Vatican. He said he had worked alone, but suspicions have lingered that more people were involved.

La Repubblica and the Italian weekly Panorama last week quoted anonymous sources saying a secret report drawn up by cardinals about the Curia had found instances of corruption in the bureaucracy as well as blackmail against gay clergymen.

The Vatican has denied the rumours and condemned the reports as an attempt to influence the outcome of the conclave via the media, comparing this to instances in history when kings and queens had tried to sway the cardinals.

Meanwhile the clergy sex abuse victims' group SNAP outlined a "dirty dozen" list of potential papal candidates and urged the Church to "get serious" about protecting children, helping victims and exposing corruption.

The organisation cited a dozen cardinals from the United States, Mexico, Honduras, Italy, Australia, Czech Republic, Canada, Argentina and Ghana accused of protecting paedophile priests and making offensive public statements.

British cardinal Keith O'Brien -- the former leader of the Catholic Church in Scotland -- recused himself from the meeting last month and admitted to sexual misconduct with young seminarians and priests in the 1980s.

SNAP also published a list of its "least worst" papal candidates, including Philippine Luis Antonio Tagle, Austria's Christoph Schoenborn and Diarmuid Martin from Ireland.