Italian authorities have discovered a ship that was sunk by the Mafia off the coast of southern Italy with 120 barrels of radioactive waste on board, a local prosecutor said Monday.

The 110-metre long ship was found on Saturday 500 metres under water and around 28 kilometres from the coast of Calabria, Paola city prosecutor Bruno Giordano said. "For the moment, we do not know the origin of the waste, but it is probably from abroad. It is a first lead," he said.

The Cunsky is one of 32 vessels carrying toxic material that has been sunk by the Mafia in the Mediterranean, according to the prosecutor's office in Reggio Calabria.

The location of the Cunsky was revealed by a Calabrese Mafia turncoat, Francesco Fonti, who confessed to being behind the explosion that brought the ship down, officials said.

Sebastiano Venneri, vice president of the environmental group Legambiente, said former members of the Ndrangheta Mafia have said that the crime syndicate was paid to sink ships with radioactive material for the last 20 years.

"An investigation on the origin of this waste is therefore necessary as soon as possible," Mr Venneri said.