(updates previous) Rome, June 3 - An Italian Senator is reportedly under investigation in relation to a probe into a fraud that allegedly saw 22 million euros siphoned away from Italy's social-security agency INPS and the justice ministry. Judicial sources said four people were arrested in an operation linked to the probe on Monday after initial reports said six people had been detained. The four, who are thought to include lawyers and civil servants, are suspected of criminal association, fraud against the State, deception and money laundering. INPS is the fund workers pay into for their retirement pensions. It also handles many benefits, such as disability and unemployment benefits.