75-year-old, Berlusconi has been accused of having intimate relationship with the girl Karima El Mahroug, also known as Ruby when she was only 17 during his infamous 'bunga bunga' parties at his villa near Milan.
"In February 2011, judges set a trial date for Prime Minister Silvio Berlusconi for the alleged commercial sexual exploitation of a Moroccan child," the report said.
The media reports cited the "evidence of third party involvement in the case."
The authors of the report concluded that "the girl was a victim of trafficking".
"During the reporting period, the country's (Italy) prime minister was investigated for facilitating child prostitution," said the report published in the US Department of State website.
Opposition have called the inclusion of Italian PM as "another shameful insult" to the country.
The trial for the underage prostitution, in which Berlusconi has been indicted will be held in Nov in Milan.