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ROME (Reuters) - Italian police discovered 270 kg (600 lb) of heroin hidden in a container that arrived aboard a ship from Iran, the biggest such haul for at least 20 years in Italy, police said on Thursday.

The freighter had set sail from the Iranian Gulf port of Bandar Abbas and stopped off in Hamburg, Germany and Valencia, Spain before reaching the Italian port of Genoa on Oct. 17, where police discovered the heroin stashed away in a consignment of Bentonite clay.

A police spokesman said investigators were not sure when or where the drugs were brought onto the ship.

Police allowed a small portion of the illicit cargo to continue its planned journey by truck to the Netherlands.

They tracked the vehicle as it crossed Switzerland, France and Belgium before reaching the Dutch town of Roosendal.

When the vehicle pulled into a warehouse on Nov. 2, Italian and Dutch police raided the premises and arrested two men of Turkish origin. The truck driver apparently did not know heroin was in his rig, police said.

“The investigation continues in order to trace the entire network that manages the drug trade, which shows, once again, that the port of Genoa is an important crossroads for drug shipments destined for the rest of Europe,” a statement said.