ROME, June 8 (Reuters) - Italian prosecutors put Israel's far-right National Security Minister Itamar Ben-Gvir under investigation over the treatment of activists who were part of a Gaza flotilla last month, a judicial source said on Monday. The source, who asked not to be named, confirmed earlier reports by Italian news agencies and said Ben-Gvir was being investigated on suspicion of torture and kidnapping of Italian citizens who were among the activists. If the probe determines charges are warranted, prosecutors could lodge a formal request for trial.