A Sicilian mafia boss serving a life sentence bit off and swallowed a prison guard's finger during an altercation, an Italian news report said on Tuesday.

Guiseppe Fanara, 60, who was serving a life sentence at Rome's Rebibbia prison, attacked seven guards in June when they came to inspect his cell, the daily Il Messagero reported.

Fanara, from Sicily's notorious Cosa Nostra clan, was nine years into his sentence under Italy's tough "41-bis" penal code reserved for mafia members.

The harsh prison regime isolates mobster bosses entirely to prevent them from running their clans from behind bars.

"During the altercation he (Fanara) bit off the agent's little finger on his right hand," the paper said. "The finger disappeared, leading a Rome prosecutor to conclude it had been eaten," it added.

The prisoner then charged the six other guards, using a broomstick as a weapon, allegedly shouting "I'll slit your throats like pigs!"

Fanara has since been transferred to Sardinia's high-security Sassari prison, the paper said, adding he was facing new charges including aggravated assault and resisting arrest. Earlier this year Italy decided to release elderly and infirm mobster bosses -- including some belonging to the influential Cosa Nostra.

That decision sparked an outcry, forcing the justice ministry to backpedal and review the release decision.