Berlusconi cannot be prosecuted while he stays in office

They want the new law tested in Italy's constitutional court.

The law was passed by parliament last week, giving the prime minister and four other top officials immunity from prosecution as long as they remain in office.

It had the effect of immediately halting Mr Berlusconi's corruption trial in Milan, where the tycoon and politician stands accused of bribing judges.

This clearly and totally violates the principle that everyone is equal in front of the law Ilda Boccassini Public prosecutor

Mr Berlusconi had been due to appear at the lengthy trial on Wednesday, to continue the evidence he gave last week.

But the new law meant he no longer had to attend.

Furious public prosecutors said the law breached some of the basic tenets of Italian justice.

"This clearly and totally violates the principle that everyone is equal in front of the law," Ilda Boccassini told the court.

'Incredible threats'

Ms Boccassini said she had "incredible threats" on a daily basis from people who had "probably" voted for Berlusconi.

She also confirmed that the trial would almost certainly never be resumed, because by 2006 - the earliest Mr Berlusconi is expected to leave office - too much time will have elapsed from the date of the alleged office for the trial to be legally possible.

Another prosecutor, Gherardo Colombo, said several fundamental principles had been violated, including equality among citizens.

A decision on whether to appeal to the constitutional court is expected to be taken in Milan on Thursday.

Charges denied

Mr Berlusconi denies paying judges to decide in his favour in a 1980s take-over battle for a state-owned food group.

The immunity law was pushed through parliament as Mr Berlusconi prepared to lead Italy into its six-month EU presidency, which starts next week.

The timing brought criticism that the legislation was timed to avoid possible embarrassment to Mr Berlusconi during his spell in the world spotlight.

Opponents of the law are attempting to raise 500,000 signatures for a petition which would force a referendum on the law.