Pope Francis’s crusade against corruption has made him a target for Italy’s all-powerful mafia clans, a leading anti-mob prosecutor has warned.

Nicola Gratteri, who has battled Calabria’s shadowy ’Ndrangheta mafia, said on Wednesday that Francis’s attempt to bring transparency to the Vatican was making the white collar mobsters who do business with corrupt prelates “nervous and agitated”.

He told the Italian daily Il Fatto Quotidiano: “Pope Francis is dismantling centres of economic power in the Vatican.

“If the bosses could trip him up they wouldn’t hesitate. I don’t know if organised criminals are in a position to do something, but they are certainly thinking about it. They could be dangerous.”

Francis, who has called for “a poor church”, has backed reform at the Vatican’s bank, which has been suspected for years of being a channel for the laundering of mob profits. This week police impounded a luxury hotel on Rome’s Janiculum hill – formerly a monastery – which the ’Ndrangheta allegedly purchased from a religious order.

In a fiery sermon on Monday, Francis railed against corruption and quoted the Bible’s advice that practitioners be thrown into the sea with a millstone tied around their neck.

“The mafia that invests, that launders money, that therefore has the real power, is the mafia which has got rich for years from its connivance with the church,” said Gratteri. “These are the people who are getting nervous.”

Gratteri attacked priests and bishops in southern Italy who legitimise mobsters. “Priests continuously visit the houses of bosses for coffee, which gives the bosses strength and popular legitimacy,” he said. A bishop in Locri in Calabria had excommunicated mobsters after they damaged fruit trees owned by the church, he said. “But before that episode, the bosses had killed thousands of people” without being sanctioned, he added.

Boosting the strong links between mob and church is the fierce religious devotion of the gangsters themselves, he said, adding that in his 26 years as a magistrate he had never raided a mafia hideout which did not contain a religious image. “There is no affiliation rite that does not evoke religion. ’Ndrangheta and the church walk hand in hand,” he said.

A survey of jailed mobsters had revealed that 88% were religious, he added. “Before killing, a member of the ’Ndrangheta prays. He asks the Madonna for protection.”

Gratteri said mobsters did not consider themselves wrongdoers, and used the example of a mafioso putting pressure on a business owner to pay protection money, first by shooting up his premises, then by kneecapping him. “If the person still refuses, the mobster is ‘forced’ to kill him. If you have no choice, you are not committing a sin.”

•Credit (text only): The Guardian of London. Photo shows Pope Francis.