Italian police launched a nationwide sweep through the homes of suspected Islamic militants, detaining 174 people for questioning.
200 search warrants were issued from Milan to Naples in an operation police said had been planned many weeks earlier.
Interior minister Giuseppe Pisanu said the operation had been preventive, targetting circles that represented a potential threat.
On Tuesday Pisanu called for stronger security laws, warning that terrorism was “knocking on Italy’s door.”
Italy has been on edge since last Thursday’s London blasts that killed at least 52 people.
Meanwhile an Italian court sentenced two men to prison terms on terrorist charges.
Mohamed Rafik, a Moroccan, and Kamel Hamroui, a Tunisian, were found guilty of plotting to attack a Milan subway station and a church in the northern city of Cremona three years ago.
They were accused of belonging to a radical Islamist group suspected of having links to al-Qaeda.