MILAN (Reuters) - An envelope containing a suspicious white powder and threats to President Giorgio Napolitano and former premier Silvio Berlusconi were sent to the Milan headquarters of major newspaper Corriere della Sera on Monday, a police spokesman said.

He said another envelope containing a grey powder was sent to the Milan offices of Il Giornale, a daily owned by the Berlusconi family. Il Giornale made no mention of any threats.

According to Corriere della Sera, a short message in the envelope said "Berlusconi and Giorgio Napolitano will be killed. Traitor to the homeland".

The message was signed by the "Armed Group for the Defence of the People", Corriere della Sera said.

Il Giornale said that after the letter sent to it was opened, six people were taken to hospital for precautionary checks.

At the beginning of April a parcel bomb was sent to the offices of La Stampa newspaper in Turin, with an anarchist group claiming responsibility. The bomb did not explode because its detonator was defective.