Milan, June 25 - The 32 witnesses who testified in ex-premier Silvio Berlusconi's defence in a trial where he was convicted of sex with an underage prostitute are likely to be probed on suspicion of perjury, judicial sources said Tuesday. Berlusconi was found guilty Monday of paying Karima 'Ruby' El Mahroug for sex and abusing his office to cover it up. He was sentenced to seven years in prison and banned for life from public office - a conviction Berlusconi's lawyers have said he will appeal. The defence witnesses, who include a junior minister in the unprecedented left-right government backed by Berlusconi, will "automatically" be placed under investigation when Milan judges issue their explanation for the verdict in September, sources said. El Mahroug, a former nightclub dancer better known under her stage name Ruby Heartstealer, denied at a separate pimping trial that she slept with Berlusconi. But she did not testify at the Ruby trial and is not on the list. It includes three members of Berlusconi's centre-right People of Freedom (PdL) Party - Deputy Foreign Minister Bruno Archi, MP Valentino Valentini and MEP Licia Ronzulli. Left-wing opponents of centre-left Premier Enrico Letta's government have called for Archi to quit. Carlo Rossella, chairman of the Medusa Film company - part of the media empire controlled by the Berlusconi family - is on the list, as is Giorgia Iafrate, the police officer who ignored a recommendation from a juvenile court official and released Ruby to Berlusconi's former dental hygienist and then PdL Lombardy regional councillor Nicole Minetti. Berlusconi was convicted of abusing his office as premier to get Ruby freed after she was detained on a 3,000-euro theft claim made by a former friend. He said he wanted to avoid a diplomatic incident because Ruby was the niece of former Egyptian president Hosni Mubarak. She has admitted to posing as Mubarak's niece. Prosecutors also say 18 among 32 young women who took part in Berlusconi's parties perjured themselves. The women, like Archi, Rossella and the others, supported the former premier's claim that the gatherings were not 'bunga bunga' sex parties but innocent and merry affairs featuring burlesque performances.