Italian Prime Minister Mario Monti, politicians and newspaper editors have been sent letters containing bullets and threats over government austerity measures, police said on Friday.

In the latest episode of mailed threats in Italy, police said they intercepted 10 envelopes at a postal sorting office in Catanzaro in the southern region of Calabria.

Each envelope contained a bullet and a letter signed by a group calling itself the Armed Proletarian Movement with insults and threats regarding austerity measures, a police spokesman said. Investigators said the group had been unknown previously.

Italy's government won a confidence vote in the lower house of parliament on Friday over a 33 billion euro ($43 billion) austerity package including spending cuts, tax hikes and pension reform aimed at shoring up public finances and calming Europe's debt crisis.

Welfare Minister Elsa Fornero, who has outlined planned pension cuts in recent weeks, former Prime Minister Silvio Berlusconi and Democratic Party leader Pier Luigi Bersani were among the politicians the letters were addressed to, police said.

Other letters were addressed to editors of major newspapers including Corriere della Sera and La Repubblica.

Local prosecutors have opened an investigation into the letters, which were unstamped when intercepted.

Police have stepped up their monitoring efforts after an Italian anarchist group claimed responsibility for two letter bombs sent last week.

The first one, to Deutsche Bank chief executive Josef Ackermann, was discovered before it was opened. The second blew up in the hands of the chief of an Italian tax collection agency. He lost part of a finger and suffered injuries to his eyes.

Another letter bomb was discovered at the tax agency on Thursday.

An anonymous parcel containing explosives found and safely disposed of at the Greek embassy in Paris on Monday also appeared to have been mailed from Italy, according to an embassy spokesman.

Letters containing bullets sent to Italy's Justice Minister Paola Severino and Rome mayor Gianni Alemanno were also intercepted on Monday.

(Reporting By Roberto Landucci, writing by Catherine Hornby, editing by Philip Pullella and Alessandra Rizzo)