Italian magistrates have launched an investigation after police found the bodies of more than 60 dogs, including puppies and pure breeds, dumped by a lake in countryside outside Naples.

Officers also found the bodies of cats and rabbits. Some of the animals were found in plastic bags. Some had died recently, while others were in an advanced state of decomposition.

The Italian animal rights organisation AIDAA suggested the dogs could have been knifed by would-be entrants to the local Camorra mafia during initiation rites in order to prove their readiness to kill.

The organisation also said unscrupulous locals offering burial and cremation services for pets could have dumped the animals at the lake, near Marigliano, to save on costs.

The Camorra has a track record of dumping waste in the countryside outside Naples, notably toxic refuse from northern Italian factories which has been linked to an increase in local cancer rates.

Investigators reportedly discovered that implanted microchips used to identify dogs had been cut from the animals, making them impossible to trace and also pointing to a possible trade in chips linked to illegal animal trafficking.

The absence of teeth marks and similar wounds on the dogs meant they had not killed during bouts of dog fighting, the Italian newspaper Il Giornale said. La Repubblica suggested the dogs might have been strays put down illegally by local councils.

"We must understand how it was possible to carry out, over time, a massacre of this kind," Francesco Servino, a local ecologist, said.