The Italian postal service intercepted a mail tube containing a spent bullet overnight which was addressed to opposition leader Silvio Berlusconi, airport officials in Rome said today.
The find came after Mr Berlusconi complained of a "hate campaign" allegedly orchestrated against him by the left as Italy's campaign for the May 13 general election heats up, and said that he had received threats.
Mr Berlusconi did not file a report to the police over the alleged threats.
Analysis of the projectile found that it came from a World War-II era antiaircraft machinegun.
The mail tube was addressed to Mr Berlusconi at the Rome headquarters of his conservative Forza Italia party, and mailed from Rome's Fiumicino airport.
Leaflets, signed by the Red Brigades, an extreme-left group which was particularly active in the 1970s, and also mailed from Fiumicino had been sent to union leaders of more than 20 Italian companies earlier this week.
Extremists claiming to act in the name of the Red Brigades killed Italian union leader Massimo D'Antona, a close aide of then-prime minister Massimo D'Alema in 1999.
Their most high-profile action was the kidnapping and killing of former prime minister and Christian Democrat leader Aldo Moro in 1978.
The leaflets sent to companies ranging from the Rome, Milan and Bologna transport authorities to an Alfa Romeo plant near Milan, a company in southern Apulia and a union branch office in Sicily also contained a claim of a bomb attack against a building housing an association for US-Italian relations and an international affairs institute.
The attack in central Rome on April 10 was claimed by a group calling itself "Nucleus of Proletarian Revolutionary Initiative".
AFP