ROME - Italian Prime Minister Silvio Berlusconi's lawyer denied the premier hid archaeological ruins at his Sardinian villa and said tapes purporting to show him boasting to a call girl were fake, newspapers said on Saturday.

The recordings, allegedly of Berlusconi in conversation with Patrizia D'Addario, have riveted Italy by revealing details of their purported sexual liaison. On Friday L'Espresso weekly released a further transcript in which the billionaire politician appeared to boast about tombs in the grounds of his island residence.

Under Italian law archaeological discoveries made on private property must be reported to authorities for inspection, cataloguing and possible excavation. The opposition has called for the government to clarify the matter in parliament.

Prime Minister Berlusconi would never have talked about discovering 30 Phoenician tombs in his park, because nothing like that is there or has ever been found at the villa, said Niccolo Ghedini, who is also a legislator for Berlusconi's People of Freedom (PDL) party.

The whole area was subject to an exhaustive search by judicial authorities a short time ago, including the villa and the park. Another search can be conducted at any time, he said.

The lawyer has repeatedly denied the authenticity of the tapes, branding them a product of the imagination, and warned that it is illegal to post or publish them.

Berlusconi, a 72-year-old self-made media mogul, has not denied that D'Addario went to his home but has said that he did not know she was an escort and that he has never paid for sex.

After newspapers around the world published details of the transcripts, Berlusconi this week sought to shrug off the scandal with a trademark quip. I'm no saint, you've all understood that, he said at the opening of a motorway project.

An opinion poll published on Tuesday showed his approval rating falling below 50 percent for the first time since he won a landslide election victory last year. It has fallen by four percentage points since May when his wife filed for a divorce, setting off a chain of disclosures about his private life.

But many Italians profess themselves unconcerned by the premier's private life, saying it is a personal matter.

The RAI state-owned television network and Berlusconi's Mediaset network, which account for most of Italy's television audience, has largely steered clear of the scandal.

However, analysts say it could sap Berlusconi's support among Catholic voters. Avvenire, the newspaper of the influential Italian Bishops Conference, has voiced disapproval.

(Editing by Andrew Roche)