ROME, Oct 23 (Reuters) - Italy has prevented telecoms group Fastweb from signing a supply deal with Huawei for its 5G core network, two sources close to the matter said, the clearest sign yet Rome is adopting a tougher stance against the Chinese telecoms equipment maker. (Reporting by Giuseppe Fonte and Elvira Pollina; Additional reporting and editing by Giselda Vagnoni; Editing by Jan Harvey)