Mr Fassino denies taking bribes in the Serbia Telekom purchase

Mr Berlusconi called in the lawyers against Democrats of the Left leader Piero Fassino after Mr Fassino alleged the prime minister was behind a series of bribery accusations against left-wing politicians.

Mr Fassino said at the weekend Mr Berlusconi was "the puppet master" behind accusations that members of the 1997 left-wing government accepted bribes during the acquisition of a stake in Serbia Telekom.

The allegations have implicated the then Prime Minister Romano Prodi, former Foreign Minister Lamberto Dini as well as Mr Fassino, who was then a minister in the Prodi government. All deny the claims.

The left has accused Mr Berlusconi of co-ordinating the allegations in an attempt to divert attention from his own legal battles over corruption.

And critics claim the allegations have been orchestrated to smear Mr Prodi - currently President of the European Commission but widely tipped to lead the left against Mr Berlusconi at the 2006 elections.

Disastrous deal

The allegations surfaced when a wheeler-dealer businessman, Igor Marini, accused the former government of taking vast bribes during the purchase of a 27% stake in Serbia Telekom - then under the control of Slobodan Milosevic's government.

We believe the sum of 15m euros is proportionate to the gravity of the remarks, the high profile of the person who made the comments and of the one who suffered from them Fabio Lepri Lawyer for Silvio Berlusconi

But Mr Marini, who is in jail while he is investigated over separate money laundering and fraud charges, has so far failed to produce any evidence for his claims.

Mr Prodi has denied knowledge of any foul play and offered to appear in front of a parliamentary commission to defend his reputation.

And at the weekend, Mr Fassino hit back, accusing Mr Berlusconi of orchestrating Mr Marini's claims:

"Marini is not the problem, Marini is a puppet, we want to know who the puppet masters are. The puppet master is in [the prime minister's residence] Palazzo Chigi," Mr Fassino told a party rally.

That in turn incensed Mr Berlusconi.

"We believe the sum of 15m euros is proportionate to the gravity of the remarks, the high profile of the person who made the comments and of the one who suffered from them," Mr Berlusconi's lawyer Fabio Lepri said.

The Serbia Telekom deal turned out to be disastrous for Italy.

In 1997 it paid about $500m for the stake - a much needed cash injection for the Milosevic regime. But when Telecom Italia sold the stake back to Serbia last year, it got only around $200m.