Pope Francis has excommunicated members of the Italian mafia on Saturday, calling them people who adore the devil.

"Those who in their lives follow this path of evil, as mafiosi do, are not in communion with God. They are excommunicated," the Roman Catholic pontiff said in scathing attacks on organised crime during a trip in one of Italy's most crime-ridden areas. "This evil must be fought against, it must be pushed aside. We must say no to it."

A person declared excommunicated becomes an exile from Catholic society. The person cannot attend public Mass nor receive the Eucharist or any other sacrament.

Pope Francis issued the strong remarks at the end of a trip to a territory controlled by the powerful 'Ndrangheta mafia. A three-year-old who was shot dead in the area in an apparent mob hit over money early this year.

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"It must never again happen that a child suffers in this way," the pope said.

According to the USA Today, the 'Ndrangheta, less well-known internationally than the Sicilian Mafia, is "Italy's most entrenched organized crime organization, in part because its reliance on family ties rather than friendships or ceremonial rites makes it difficult for police to infiltrate."

"The organization has operations that stretch as far as Australia and Germany, resulting in annual revenue in the range of $75 billion - around 3.5 per cent of Italy's gross domestic product - according to Demoskopika, a research firm based in Calabria."

Nicola Gratteri, a senior 'Ndrangheta investigator, one of many prosecutors who lives under constant police protection, told newspaper Il Fatto Quotidiano that the pope's remarks was a very courageous one.

"This was a courageous speech and one that we've been waiting for more than a century . . . This is an invitation to all Catholics and an order to all priests and bishops. No more ambiguity in relations with mafia bosses."

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However, it is most certain that Pope Francis could become a target for the group, Gratteri said.

"The pope's reform agenda was making the 'Ndrangheta very nervous... The pontiff's warnings about excommunication should resonate strongly in the region. The 'Ndrangheta is also highly religious, often paying for Roman Catholic Church initiatives and seeking the blessings of local priests, who will change their plans on short notice to officiate at mob weddings, funerals and baptisms. Sometimes, religious processions will pause in front of the homes of 'Ndrangheta leaders in order to bless the inhabitants," he said in the USA Today.