Italian mobsters planning a bomb attack on a top prosecutor leading the fight against the Camorra Mafia in Naples have been arrested by police, according to local media reports citing anonymous investigative sources.

The Camorra, based in and around the southern city, is one of Italy's main Mafia organisations.

The target was allegedly Giovanni Colangelo, Naples chief prosecutor.

The ANSA news agency said 550 grams of TNT was found on Friday hidden in the garden of Amilcare Monti Condesnitt, a jailed mobster from Gioia del Colle, a town in southern Italy where Colangelo has a home.

The explosives were meant to be used to kill the prosecutor.

Prosecutors in Bari investigating the allegations were given the information by an informant held in the same jail as Condesnitt, ANSA said.

Police were led to the TNT by tapping phones during an investigation in February into an attempted murder linked to Mafia turf wars in Bari.

Once a connection to Colangelo was established, officers seized the TNT and arrested five people.

"I wish to express my solidarity, support and respect for prosecutor Colangelo. He is an excellent magistrate," Giovanni Legnini, deputy leader of the governing body of the Italian judiciary, said in reaction to the reports.

For his part, Colangelo's office issued 11 arrest warrants on Wednesday against alleged members of the Camorra Mafia suspected of running illegal gambling and sports betting activities and an extortion racket.

The same day, Italy's tax police seized assets worth more than $17m belonging to Nicola Schiavone, a jailed leader of the Casalesi, one of the Camorra's bloodiest crime families.

Italy has a history of Mafia murders against top-level officials.

The most notorious cases were in 1992 when two separate bombs planted in Palermo by Sicily's Cosa Nostra killed anti-Mafia prosecutors Giovanni Falcone and Paolo Borsellino.