Italian gangs have used RDX explosives in the past but police say they are not behind the latest shipment [EPA]

Italian police have seized seven tonnes of the powerful RDX explosives from a container ship believed to be on its way to Syria, according to authorities.

Anti-mafia police found the explosives hidden in a shipment of powdered milk at the port of Gioia Tauro in southern Calabria, Italian news agencies reported.

Carmelo Casabona, the region's police chief, said investigators are not yet sure of who was in control of the shipment, but it appeared that it originally travelled from Iran.

Also known as T4, RDX is a powerful military grade explosive that has been used in several devastating attacks believed to have been carried out by the Italian mafia in past years.

It was most notably used in the assassinations of anti-mafia judges Giovanni Falcone and Paolo Borsellino, the former being blown up with his wife and three bodyguards after a bomb was detonated under a motorway.

Casabona said the cargo had "the involvement of international criminal organisations," but ruled out the involvement of local mafia, know as the Ndrangheta, saying the shipment was too large.

The cargo was reportedly found on a Liberian-registered ship called the Finland, which is owned by an Italian-Swiss company, MSC.

However the company has not yet confirmed the story to the media.

Source: Agencies