The Vatican has rejected claims that Pope Francis has failed to speak out against human-rights abuses during Argentina's military rule and said he had in fact helped save lives.
Jorge Mario Bergoglio, the first pope to come from Latin America, has been criticised by leftist critics for his actions during Argentina's Dirty War in which 30,000 people died or disappeared from 1976 to 1983.
His role in the arrest of two young Jesuit priests, Orlando Yorio and Francisco Jalics, who were taken to a torture centre by the ruling junta, has come under intense scrutiny.
Speaking on Friday Federico Lombardi, Vatican spokesman, said: "There has never been a credible, concrete accusation against him. The Argentinian justice system ... has never charged him with anything."
He said the campaign against Bergoglio was "well known" but claimed it was defamatory and aimed at discrediting the Church.
"The accusations come from parts of the anti-clerical left to attack the Church and must be denied," said Lombardi, insisting that Bergoglio "did a lot to protect people during the dictatorship" when he was not yet a bishop.
Bergoglio himself has always denied any involvement in the case, and even says he intervened with the head of the junta, Jorge Videla, to beg for them to be freed. The two men were released after five months.
The newly elected pontiff, who is also the first Jesuit pope, earlier urged the Catholic Church that he has inherited not to succumb to "pessimism" and to find new ways of spreading the faith.
"Let us not give in to pessimism, to that bitterness that the devil offers us every day," he told an audience of the world's cardinals on his third day in office.
In a reference to the declining number of worshippers in many parts of the world, he urged the cardinals to find "the courage to persevere and also to find new ways to bring evangelisation to the ends of the earth".
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Francis, 76, said he and they were "elderly", but old age brought wisdom.
"Let us give this wisdom to young people like good wine that gets better over the years," he told the cardinals.
Francis hailed his predecessor Benedict XVI's historic resignation as a "courageous and humble act".
Benedict, who last month became the first pope to stand down for 700 years, had "lit a flame in the depth of our hearts that will continue to burn", he said.
Francis wore white papal vestments but also plain black shoes, not the red shoes favoured by his German predecessor, for the address in the ornate 16th-century Clementine Hall in the Apostolic Palace at the Vatican.
He has indicated that he will lead a more simple papacy, stripped of the fineries enjoyed by his predecessors.
On Thursday, he gave a stark warning that the Church, wracked by scandal and Vatican infighting, risked becoming just another charitable organisation if it strayed from its true mission.