Italian Prime Minister Silvio Berlusconi is being investigated over his dealings with a 17-year-old nightclub dancer.Mr Berlusconi is suspected of abusing his power by trying to have the Moroccan girl - known by her stage name Ruby - released from a police cell.
Some reports say the probe includes allegations of underage prostitution.
Lawyers for the 74-year-old prime minister dismissed the claims as "absurd and groundless".
They said the allegations had already been refuted by all witnesses and people directly involved.
Leader's legal woes Mr Berlusconi has previously admitted calling the police on her behalf, but says he did nothing wrong.
Italian newspaper Corriere della Serra reported that prosecutors would investigate whether Mr Berlusconi had made the call in order to hide his use of underage prostitutes.
The dancer, now 18 years old, told newspapers she was paid 7,000 euros (£5,900; $9,400) after she attended a party held by Mr Berlusconi last year.Ruby, whose real name is Karima El Mahroug, has denied having sex with him.
She was being questioned over theft allegations when Mr Berlusconi called the police on her behalf.
He apparently told them that she was a relative of Egypt's President Hosni Mubarak.
The case came to light last November, and prosecutors at the time questioned Milan police over Mr Berlusconi's involvement.
In a statement on Friday, Milan prosecutors said they had issued a summons to Mr Berlusconi.
The prosecutors said they were investigating alleged crimes committed between February and May 2010, but gave few details of the allegations.
The investigation is the latest in a string of legal difficulties for Mr Berlusconi.
On Thursday, a law shielding him from three unrelated trials was significantly watered down by a ruling of Italy's Constitutional Court.
He could eventually face trials for bribery and fraud related to his business dealings.
Mr Berlusconi told reporters in Berlin on Wednesday that he found the Constitutional Court hearing "laughable".
The prime minister has argued he is the target of left-wing prosecutors.