The 38-year-old who is a legal immigrant and married with three children, was arrested in the Sardinian town of Macomer by hooded police, who forced him from his car as he left his home.
He is accused of association with the aim of international terrorism.
Police said they had been tracking him since September, after his cousin was detained in Lebanon where he was accused of trying to poison a water tank used by the army.
They said the man referred to his cousin’s purported plans to carry out a toxic attack in Italy during a confession.
Amin had tried to buy poison over the internet, police said, but there was no evidence he had actually managed to purchase the materials.
The Lebanese man of Palestinian descent had recently withdrawn all his money from the bank and was searching for his passport, said Italy’s chief anti-terrorism prosecutor, Federico Cafiero De Raho.
“He must have been close to doing something,” he added.
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