MILAN (Reuters) - The prosecutor in former Italian prime minister Silvio Berlusconi's sex trial has received a series of anonymous letters of threats, including one with two bullets, Milan's chief prosecutor said on Thursday.

The letters against Ms Ilda Boccassini have become more frequent since she requested a six-year jail sentence and a lifetime ban on holding public office for Berlusconi, Mr Edmondo Bruti Liberati said.

"In the last few weeks there has been a crescendo of anonymous letters containing serious threats against Boccassini, including one yesterday containing two bullets," Mr Bruti Liberati said in a statement.

On May 13, Ms Boccassini requested the jail sentence and public office ban for Berlusconi, who is charged with paying for sex with a Moroccan nightclub dancer when she was a minor and abusing his office to have her released from police custody.

In a six-hour-long closing argument, Ms Boccassini said the so-called "bunga bunga" parties at the villa of the 76-year old billionaire media tycoon involved a "system of organised prostitution".

Berlusconi has denied the charges.

The verdict is expected on June 24.