Roberto Saviano, a writer and expert on organized crime in his hometown of Naples, has been under 24-hour protection since his book came out in 2006. Roberto Saviano, a writer and expert on organized crime in his hometown of Naples, has been under 24-hour protection since his book came out in 2006. (Salvatore Laporta)

Italian police have stepped up their investigation into reports the mafia in Naples plans to carry out a threat to kill the author of the bestseller Gomorra by Christmas.

"We've launched an inquiry to verify the truth behind this news," Franco Roberto, a co-ordinator of the local anti-mafia squad for Naples, told Reuters.

Since the publication of his book in 2006, Roberto Saviano has been in hiding and living with round-the-clock protection.

The Naples-born writer based the book on his own investigations of the Camorra, as the mob in his hometown is known. His account has sold 1.2 million copies in Italy and been translated into 42 languages.

Gomorra is now a movie that has been entered into the foreign film category of the Oscars. It captured second place at this year's Cannes Film Festival.

Italian papers said the Naples mob's Casalesi clan had upgraded its threat to "operative" mode and wants Saviano dead by Christmas.

The Camorra is omnipresent in every corner of life in the southern city of Naples: from the protection racket to drug running and even waste disposal, as Saviano's book details.

The 27-year-old author appeared on an Italian radio show Monday, describing his life in hiding.

"Many days are terrible," said Saviano, who spends some of his time boxing with escorts "who sometimes call me 'captain.'"

He contends the mafia is worried that millions of people have bought his book.

"It's the readers who have frightened the crime bosses, not me," said Saviano.

With files from Reuters