VATICAN CITY – Pope Benedict said in a historic announcement he no longer had the mental and physical strength to run the Roman Catholic Church and would become the first pontiff in more than 700 years to resign, leaving his inner circle “incredulous.” Church officials tried to relay a climate of calm confidence in the running of a 2,000-year-old institution but the decision could lead to one of the most uncertain and unstable periods in centuries for a Church besieged by scandal and defections. The Church has been rocked during Benedict's nearly eight-year papacy by child sexual abuse crises and Muslim anger after the pope compared Islam to violence. There was scandal over the leaking of the pope's private papers by his personal butler. In the announcement read to cardinals in Latin, the German-born pope, 85, said: “Well aware of the seriousness of this act, with full freedom I declare that I renounce the ministry of Bishop of Rome, Successor of St Peter ... “As from 28 February 2013, at 20:00 hours (1900 GMT) the See of Rome, the See of St. Peter will be vacant and a conclave to elect the new Supreme Pontiff will have to be convoked by those whose competence it is.” A new leader of the world's 1.2 billion Roman Catholics could be elected as soon as Palm Sunday, on March 24 and be ready to take over by Easter a week later, he said. “This is disconcerting, he is leaving his flock,” said Alessandra Mussolini, a parliamentarian who is granddaughter of Italy's wartime dictator.– Agencies (See also P8)