Italian customs have seized up to seven tonnes of the powerful explosive RDX.
The find was made in Gioia Tauro in Calabria, having arrived from Iran. It was hidden in bags of powdered milk and destined to be re-shipped to Syria.
RDX is generally reserved for military and industrial use and investigators do not believe the mafia to be the end users of the newly-seized batch.
The substance has been used by the Cosa Nostra in Italy before, notably in the assassinations of anti-mafia judges Giovanni Falcone and Paolo Borsellino.