Italian authorities on Saturday arrested a 38-year-old Chechen accused of fighting with the Islamic State group in Syria and participating in a deadly attack on foreign and Russian journalists in Chechnya.
Prosecutors said in a statement that Eli Bombataliev was being held on terror charges.
They said evidence indicates that he was part of an Islamic State network based in Belgium.
It was not clear how long he had been in Italy.
As part of the operation, authorities expelled two Albanian brothers in their 20s legally residing in Italy and a 49-year-old Russian woman in the country illegally.
They were allegedly being trained by the Chechen.
According to police, the Russian woman was being prepared to act as a suicide bomber.
Prosecutors said evidence indicates Bombataliev participated in an attack on journalists in Grozny, Chechnya in December 2014 that left 19 dead and that he fought in Syria in 2014 and 2015.