(By Denis Greenan). Milan, June 25 - Supporters of Silvio Berlusconi staged a protest in Rome on Tuesday after judges found the ex-premier guilty Monday for paying for sex with an underage prostitute and abusing his office as then premier in an attempt to cover it up. "Rome, Piazza Farnese. Resist puritanical justice," read a front-page headline in the right-leaning Il Foglio daily, which is edited by Giuliano Ferrara, a close friend of the three-time premier. "This is a shameful sentence that hurts Italian justice and lowers it to the level of that in Afghanistan or Iran," he said. In a closely watched verdict Monday, judges in Milan sentenced Berlusconi to seven years in prison and banned him for life from holding public office, rulings he will appeal. "This is a violent sentence," said Berlusconi. "I will resist the persecution. I was convinced I would be acquitted". Berlusconi and Karima 'Ruby' El Mahroug, the underage dancer he was found guilty of paying for sex in 2010, both denied ever having sex. Berlusconi's supporters Tuesday echoed his oft-made allegations of a leftist judiciary out to get him and chided Premier Enrico Letta of the centre-left Democratic Party (PD) for not speaking out in support of the former premier and media magnate, whose centre-right People of Freedom (PdL) party occupies important seats in the administration. "(One would have expected) not only words of personal solidarity with Berlusconi, a victim of unjust persecution," but also a "political assessment" on the necessity to restore a "correct balance" between the powers of government, said PdL Coordinator Sandro Bondi. Letta was set to meet Berlusconi Tuesday evening with the verdict and its repercussions high on the agenda, political sources said. Reservations among PD left-wingers about the alliance with Berlusconi have been heightened by the Ruby verdict. Former PD chair Rosy Bindi posted a statement asking "how long can a party with respect for the rule of law in its DNA stay in coalition with a leader who has already piled up several extremely grave verdicts, who demands impunity in the name of his electoral legitimation and misses no opportunity to attack the magistrature". PdL MP Francesco Paolo Sisto, head of the House Constitutional affairs committee, said the "tensions" aroused by the sentence, "which are currently still outside the executive, may eventually affect how long it lasts". Many have worried that the fragile stability of the unprecedented coalition, which makes strange bedfellows of long-time foes who finished first and second in February's inconclusive general election, was at risk over the legal troubles of Berlusconi, who has threatened to withdraw support over other issues. Members of his party have vowed to resign from government en masse if their leader's ban from office is upheld at the supreme Court of Cassation. Italian President Giorgio Napolitano issued an appeal for calm Tuesday and said he was irked by constant speculation the government might fall. Napolitano, who is also the titular head of the judiciary's self-governing body, the CSM, called for greater respect of all branches of the State. "We must always respect and safeguard public institutions, which are the bedrock of the life and development of a democratic State and civil society worthy of the name," said Napolitano. "It's not possible to talk about a government crisis after just two months (in office)," the president went on. "I'd like to see a bit more continuity in government institutions," he said, adding that "we in Italy hold the record for political turmoil". The Ruby verdict was at the court of first instance and it will take years to reach a conclusion at the supreme Court of Cassation. But Milan prosecutors have already said they want to probe Berlusconi's defence witnesses for suspected perjury. The 32 witnesses who testified in his defence, who include a junior minister, will "automatically" be placed under investigation when Milan judges issue their explanation for the verdict in September, judicial sources said Tuesday. El Mahroug denied at a separate pimping trial that she slept with Berlusconi. She did not testify at the Ruby trial and is not on the prosecutors' 'perjury' list. But it includes three PdL members - Deputy Foreign Minister Bruno Archi, MP Valentino Valentini and MEP Licia Ronzulli. Left-wing opponents of Berlusconi and of Letta's government on Tuesday called for Archi to quit. Carlo Rossella, chairman of the Medusa Film company - part of the Mediaset media empire controlled by the Berlusconi family - is also on the list. Another likely suspect 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, who was accompanied by the Brazilian prostitute who phoned Berlusconi in Paris to say Ruby was in trouble. 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, as he mistakenly believed at the time, the niece of former Egyptian president Hosni Mubarak. Ruby, in statements taken down as evidence, has admitted to posing as Mubarak's niece and said she told "a pack of lies". Of the more than 30 young women who admitted taking part in Berlusconi's parties, 18 took the stand and, prosecutors say, allegedly 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, jolly affairs featuring burlesque performances. The Ruby case is not the most immediate of Berlusconi's legal worries because he faces a final verdict over tax fraud at Mediaset later this year. An appeals court recently upheld a four-year term and a five-year ban from office which, if confirmed, could see him booted out of parliament. But the PdL is already making overtures to PD members who want an end to what the ex-premier calls a 20-year "war" against him to come up with an immunity law similar to ones which have been struck down in the past by the Constitutional Court.