Gianluigi Nuzzi, one of two Italian journalists facing a criminal probe over leaks from the Vatican, said Monday he would defy a summons to be interrogated by Holy See prosecutors.

Under the hashtag #Noinquisition, Nuzzi said on his website that he had decided not to appear as requested on Tuesday because Vatican law did not guarantee his right to publish news in the public interest while protecting his sources.

"Revealing secret news (in the Vatican) does not earn a medal, as happens for the free press in the entire democratic world, instead it is always, and in every case, a crime," Nuzzi wrote.

The journalist went on to question why the Vatican was investigating him and a colleague rather than looking into the serious allegations of financial malpractice made in his just-published book, "The Merchants in the Temple".

The Vatican announced last week that it was investigating Nuzzi and another reporter Emiliano Fittipaldi for divulging the content of confidential Vatican documents, in breach of a law adopted by the Holy See in 2013.

The legislation was introduced by Pope Francis after the Vatileaks scandal which saw his predecessor Benedict XVI weakened by leaks to the media orchestrated by his own butler.

Nuzzi and Fittipaldi's books use classified documents to back up depictions of corruption, theft and uncontrolled spending at the Vatican.

They notably claim charity money was spent on refurbishing the houses of powerful cardinals and that the Vatican bank continues to shelter suspected criminals.

Vatican officials have dismissed the content of the books as either inaccurate or out of date, insisting that reforms instigated by Pope Francis have addressed some, if not all, of the irregularities highlighted.

Angel Vallejo Baldo, a Spanish priest suspected of leaking the documents, is currently in detention in the Vatican pending the outcome of the investigation.

An alleged accomplice, Italian PR executive Francesca Immacolata Chaouqui, is also being investigated but was released from custody after saying she would cooperate with the authorities.

She has since insisted that Baldo acted alone and that the priest had been behind a secret recording of Francis railing against the chaotic state of Vatican finances he inherited on becoming Pope in 2013.

Francis himself has branded the leaking of the Vatican documents as "a deplorable act which does not help."