"We are holding 300 westerners, of whom six or seven are Italian, according to the information I have. They are all converts to Islam," the source said.
"The case of Giuliano Delnevo, the 20-something from Genoa, killed fighting on the side of the rebels is not an isolated case," the source told Adnkronos.
The source was referring to the reported death in Syria of a radicalised Italian Muslim convert who allegedly went to Syria to wage holy war or Jihad.
Italian daily Il Giornale on Tuesday reported Delnevo's death citing unnamed intelligence and interior ministry sources. The paper stated Delnevo's age as between 20 and 23. It did not say where or when he died in Syria and for which rebel group he was fighting.
Prosecutors in his home city of Genoa in Italy's northwest said they had been probing Delnevo and other jihadist suspects elsewhere in the country for some time.
Anti-terrorism sources told Adnkronos they had been closely monitoring several dozen radicalised Muslims and converts to Islam in Italy.