"There are several dozen such individuals," the sources said.
"They are generally Muslim converts who use the internet to spread propaganda and communicate with other fundamentalists.
"In some cases, they decide to take direct action and join jihadist fighters."
Most of the jihadists in Italy who are being monitored by secret services are Muslim immigrants from North Africa and have been to Syria at lest once to fight alongside rebels forces, according to sources cited by Il Giornale daily.
Il Giornale on Tuesday reported Delnevo's death, citing unnamed intelligence and interior ministry sources.
The daily did not say when or where in Syria Delnevo was killed, or for which rebel group he was allegedly fighting, stating only that it had learned of his death last Friday and that he had been identified from his Italian passport.
European Union terrorism experts believe around 500 Europeans have fought against pro-Assad forces in Syria.