* Testimony in trial for three accused of aiding prostitution
* Ruby says never had sex with Berlusconi, on trial in separate case
* Says she was given envelopes of 500 euro notes
The nightclub dancer at the centre of former Italian Prime Minister Silvio Berlusconi's "bunga bunga" sex trial told a court on Friday that guests at the media tycoon's parties dressed as nuns, nurses and U.S. President Barack Obama.
Karima El Mahroug, better known by her stage name "Ruby the Heartstealer", spoke as a witness in a trial at which talent scout Lele Mora, television anchor Emilio Fede and former showgirl and regional councillor Nicole Minetti are accused of inducing and aiding prostitution.
Berlusconi is being tried separately for paying for sex with El Mahroug when she was a minor and then abusing office by having her freed from police custody after her arrest for theft.
Her appearance is nevertheless an embarrassment for the 76-year-old billionaire, serving as a reminder of the legal threats the leader of the centre-right and key partner in the governing coalition faces.
A verdict in the sex trial is expected in June, and a conviction for tax fraud is moving to a final appeal. Berlusconi says he has never paid for sex, denies any wrongdoing and says judges are politically motivated against him.
El Mahroug failed to appear as a witness at Berlusconi's trial in December because she was on holiday in Mexico. In her Friday testimony, she challenged Berlusconi's assertion that events at his villa were elegant dinner parties.
DRESSING AS OBAMA
Glamour model Marysthelle Polanco, one of 14 women who became notorious after they were discovered to be housed at a Milan address at Berlusconi's expense, dressed up as Obama and Brazilian footballer Ronaldinho, El Mahroug said.
On one occasion Minetti, Berlusconi's former dental hygienist who graduated to a career in showbusiness and politics, "dressed up as a nun ... and as she danced, she took off her clothes and was left in her underwear," El Mahroug told the court.
Wearing a large grey scarf and her hair tied back in a sleek ponytail, she entered the Milan courtroom flanked by police, walking quickly past waiting journalists. It was the first time she has testified about the parties.
El Mahroug said she received envelopes containing thousands of euros in cash from the then-prime minister and spent the night at the villa on one occasion, after which she and several other women who had slept there shared breakfast with him.
She denied ever having sexual relations with Berlusconi, and said she did not see him engaged in physical contact with other women at the parties, repeating statements she has made to the media in the past.
The Moroccan-born El Mahroug was 17 when she attended the parties at Berlusconi's villa outside Milan. She said she lied about her age and that she had told guests that she was a relative of former Egyptian leader Hosni Mubarak.
Berlusconi's defence against the abuse of office charge is that he acted under the belief that El Mahroug was related to Mubarak, and that he needed to free her from police custody to prevent a diplomatic upset.