Abdul Wahid As Siquili, a 28-year-old factory worker who converted to Islam, was arrested in Pesaro because police feared he was about to flee to Morocco, the Italian news agency ANSA reported.
Authorities conducted raids in Milan, Cuneo, Pesaro, Cagliari, Salerno and Palermo. The nationality of the 10 others being investigated was not disclosed.
Police said As Siquili had "close ties" to Mohamed Jarmoune, a Moroccan militant arrested in March for allegedly planning an attack on Milan's synagogue.
Notable deaths of 2014 [PHOTOS]