VATICAN CITY (AFP) - A Spanish priest at the centre of a controversial Vatican leaks trial admitted on Monday to passing classified documents to the press but insisted he had acted under emotional blackmail from a female colleague with whom he was romantically entangled.

"Yes, I sent documents to journalists, I handed over a list of five pages with 87 passwords," Monsignor Lucio Vallejo Balda told a Holy See court.

The Spanish Vatican official said he had not been "fully lucid" when he leaked the documents and had since been treated by a psychiatrist for depression and stress.

Vallejo Balda described his former colleague, Italian PR consultant Francesca Chaouqui, as a dangerous and manipulative woman who had cooerced him into leaking the documents by threatening to reveal an intense relationship between them.

"I was certain that there were illegitimate interests behind Chaouqui," he told the court, revealing that he believed his colleague and her husband to have been working for the Italian secret services.

Listening to her estranged former colleague give evidence, Chaouqui, who is pregnant, appeared highly agitated, repeatedly whispering to her lawyer from her seat on the accused bench.

Vallejo Balda's evidence came as the trial resumed after a three-month adjournment to enable technicians to recover deleted email, text and WhatsApp messages between him and some of the accused.

His claim that his actions were the result of a combination of sexual tension and blackmail will only confirm the view of those inside the Vatican who regard the entire case as a public relations own goal by the Church hierarchy.

As well as putting the spotlight on out-of-control spending at the top of the Catholic Church, the trial also has the potential to put some of Pope Francis's closest associates on the stand.

In December, Chaouqui was granted the right to call as witnesses Vatican number two Cardinal Pietro Parolin and two Francis confidantes, charity supremo Archbishop Konrad Krajewski and Cardinal Santo Abril y Castello, who heads a panel overseeing the scandal-hit Vatican bank.

Chaouqui is accused of conspiring with Vallejo Balda and his assistant Nicola Maio to leak data and documents they had access to as members of a commission appointed by Francis to spearhead a financial clean-up shortly after his election in 2013.

The two journalists on trial, Gianluigi Nuzzi and Emiliano Fittipaldi, have published books based on the documents at the heart of the trial.

All five accused have been prosecuted under draconian anti-leaks legislation, which could see them receive prison terms of between four and eight years.

The law was rushed onto the Vatican statue book in 2013 as a result of the fallout from the first Vatileaks scandal, which centred on secrets divulged by the butler of now-retired Pope Benedict XVI.

The Vatican has been criticised by press freedom groups for pursuing the prosecution of the two journalists, who say they were only doing their jobs by revealing problems that believers and the broader public have a right to know about.

Vallejo Balda spent nearly two months in a police cell last year and, having been released to house arrest just before Christmas, was sent back behind bars days before the resumption of the trial.

Vatican spokesman Federico Lombardi said the monsignor had "breached the conditions of his (house arrest) status by communicating with the outside."

The books published by Nuzzi and Fittipaldi depict the Vatican bureaucracy that Francis inherited three years ago as being on the verge of implosion thanks to a toxic cocktail of chronic over-spending, feeble accounting systems and serious irregularities in several departments which may have masked corruption.

One of their most striking revelations was that less than 20 per cent of donations made by believers around the world under the Peter's Pence scheme ended up being spent on good work.

The rest was swallowed up by the Vatican bureaucracy, partly helping to subsidise the luxurious lifestyles of certain Rome-based cardinals.

The books also highlight irregularities in the system for appointing saints which Francis last week moved to address - proof, the journalists say, that their work is in the Church's interest.

The case resumes on Tuesday.