Silvio Berlusconi said on Tuesday Italy's President Giorgio Napolitano lacked credibility and was unreliable in failing to safeguard Berlusconi from what he called his persecution at the hands of the judiciary.
Berlusconi's relations with Napolitano have soured steadly since the centre-right leader was convicted in August for tax fraud. His comments on Tuesday, in a letter to a magazine, are the first time he has criticised the president publicly .
They come as Berlusconi is battling to hold together his People of Freedom party (PDL), many of whom are openly dissenting from his decision to try to bring down Enrico Letta's government and push for new elections.
"Enrico Letta and Giorgio Napolitano should have realised that, by not safeguarding the political rights of the leader of the national centre-right, they were destroying an essential element of their credibility," Berlusconi told the weekly Tempi.
"How can anyone be reliable if they ... allow the main government partner to be politically assassinated by judicial means?" he said.
Berlusconi can ill afford to alienate Napolitano, who is the supreme arbiter of Italian politics and is the only person who can dissolve parliament and call new elections, as Berlusconi wants.
Napolitano has made clear his own exasperation with Berlusconi's recent steps to undermine Letta's left-right coalition government.
Last week he described as "absurd" Berlusconi's claims that the judges who convicted him were guilty of subversion or a coup d'etat and repeated that neither he nor Prime Minister Letta could do anything to change the outcome of the trial.