Italy’s former prime minister, Silvio Berlusconi, facing trial on tax fraud and sex charges and under investigation for suspected political bribery, promised to take on prosecutors after Parliament opens this week.

The leader of the People of Freedom (PDL) party has often clashed with magistrates during his two decades in politics but problems have escalated this month as his trial on charges of paying for sex with an under-age prostitute has neared its end.

“The repeated moves to open trials by magistrates, which is motivated by political prejudice can no longer be tolerated,” the 76-year-old media billionaire said in an interview with Panorama, a weekly owned by his own Mondadori publishing group.

He promised a “parliamentary battle”, accusing left-wing judges of trying to sabotage the centre right, which has the second-largest grouping in parliament following last month’s inconclusive general election.

“It’s a battle we cannot lose if we don’t want Italy to continue to be a country in which there is no assurance for anyone who dedicates themselves to public service,” he said, according to extracts from the interview, due out on Friday.

Berlusconi’s comments add to growing tensions between him and magistrates following the election which left no party able to form a government as parliament prepares to sit for the first time on Friday.

Both the centre-left and the anti-establishment 5-Star Movement of former comic Beppe Grillo have attacked Berlusconi for his persistently antagonistic comments and President Giorgio Napolitano has been alarmed by the feuding.

Earlier this week, parliamentarians from Berlusconi’s PDL protested outside the Milan courthourse where the prostitution trial is being held, prompting a warning from the president.

Napolitano issued a statement on Tuesday dismissing accusations of political bias by magistrates but calling for “respect for the strict rules of behaviour” expected of justice system officials.

Berlusconi faces a long string of legal battles over the next few weeks, starting with the trial in which he is accused of paying for sex with former nightclub dancer Karima El Mahroug, better known under her stage name “Ruby”, when she was a minor. He denies the charge and El Mahroug also denies ever having sex with him.

He is also being investigated by Naples magistrates on suspicion of bribing a senator to change sides in 2006 to help bring down the last centre-left government led by Romano Prodi by sabotaging its wafer-thin parliamentary majority.

Berlusconi has been in hospital since Friday being treated for an eye problem which has already prompted him to cancel a number of public engagements and to ask for a further delay to the prostitution trial.

A hearing in the trial, which had been due on Wednesday, has now been delayed until March 18, with further dates on March 20, 21 and 25, when a verdict is possible.

In addition, Berlusconi is appealing against a four-year jail sentence for tax fraud in connection with his Mediaset television empire.