FILE PHOTO: Forza Italia party leader Silvio Berlusconi waves to his supporters during a rally for the regional election in Palermo, Italy, November 1, 2017. REUTERS/Guglielmo Mangiapane/File Photo

TURIN, Italy (Reuters) - A prosecutor asked a court in the northern city of Turin on Friday to charge four-times prime minister Silvio Berlusconi with bribing a witness when he was being tried for paying for sex with a minor.

The case is one of seven that form part of the same issue being handled by as many different courts.

In the cases, prosecutors allege Berlusconi doled out 10 million euros ($12 million) to corrupt several witnesses at his trial in 2013, in which he was accused of having sex with 17-year-old Moroccan nightclub dancer Karima El Mahroug, better known in Italy by her stage name, Ruby the Heartstealer.

Prosecutors in Turin said Berlusconi had paid a former nurse and model, Roberta Bonasia, to give false testimony in the trial.

Bonasia is one of more than a dozen women who testified about Berlusconi's so-called "Bunga Bunga" sex parties at his plush residence near Milan, which Berlusconi says were nothing more than elegant dinner parties.

The alleged payments to various witnesses are being handled in different courts, according to the location of the banks that received the money.

El Mahroug received 7 million euros, prosecutors say.

Berlusconi was originally found guilty of paying to have sex with a minor and sentenced to seven years in jail, but the verdict was overturned in 2014 by an appeals court, which ruled that there was no proof he had known Mahroug's age.

In this case, both Berlusconi and Bonasia, whom prosecutors also want to put on trial, deny any wrongdoing. Their lawyers were not immediately reachable for comment.

The 81-year-old Berlusconi is staging a political comeback ahead of a national election due early next year. His Forza Italia (Go Italy!) party is part of a centre-right coalition that is currently leading opinion polls.

Berlusconi's political career has been dogged by non-stop legal battles. After a conviction for tax fraud in 2013, he was barred from office, but this week he asked the European Court of Human Rights this week to overturn the ban.

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(Reporting by Gianni Montani in Turin and Ilaria Polleschi Milan, writing by Steve Scherer in Rome; Editing by Kevin Liffey)