Italian Prime Minister Silvio Berlusconi was threatened on Wednesday by a mysterious militia faction through a letter addressed to the Ansa news agency.

The missive was sent by a local group called "Armed Group for Freedom" to Ansa's local office in the southern town of Bari, on the Adriatic coast. It contained a hand-written note warning that "a bomb would blow up Berlusconi's car".

Intelligence officers are investigating the danger of the missive, which follows other threats recently received by the premier.

Ahead of the March 28-29 regional elections won by Berlusconi's government center-right coalition, a missive containing a bullet and death threats had been addressed to Berlusconi and his People of Freedom Party. A bomb-pack was also sent to the premier's coalition ally the Northern League Party, injuring a postman.

The following day an envelope was sent to the premier's Milan villa containing white powder initially feared to be anthrax. The police later said it had been mailed by a man with mental problems.

The tones of the Italian electoral campaign were bitter and the fierce political wrangling between the center-right majority and the center-left opposition still rocks the country.

Berlusconi has repeatedly accused the left and the judiciary of leading a witch hunt against him. In December the premier was injured in the face at a political rally in Milan by a mentally unstable man. He was hospitalized and underwent facial and dental operations.

The climate in Italy is thus tense. On Thursday Interior Minister Roberto Maroni is expected to hold a special meeting of the national committee for public order and safety to discuss the intimidation episodes towards the premier, politicians and political parties.

In a statement, Maroni described these as "real acts of political terrorism which we intend to curb without hesitation to avoid the risk of reliving the Years of Lead and guarantee the protection of free democratic institutions."

The Years of Lead refers to Italy's terrorist period of the 1970-80s, when left and right-wing militia clashed on the streets followed the strategy of tension.