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Vatican City (CNN) -- The Vatican pushed back Friday against claims that Pope Francis failed to protect two fellow Jesuit priests who were kidnapped during Argentina's military dictatorship.
The accusations have resurfaced since the Argentine cardinal's unexpected election to the papacy two days ago.
A book by investigative reporter Horacio Verbitsky accuses Francis, who was then Jorge Mario Bergoglio and was head of the country's Jesuit order, of deliberately failing to protect the two priests, Orlando Yorio and Francisco Jalics, when they were seized by the navy. They were found alive five months later.
But the Rev. Federico Lombardi, a Vatican spokesman, dismissed the claims -- which date back to Argentina's so-called Dirty War from 1976 to 1983 -- as false and defamatory.
"The campaign against Bergoglio is well-known and goes back to many years ago. It was promoted by a defamatory publication," Lombardi said at a Vatican news conference.
"This was never a concrete or credible accusation in his regard. He was questioned by an Argentinian court as someone aware of the situation but never as a defendant. He has, in documented form, denied any accusations," said Lombardi.
"Instead, there have been many declarations demonstrating how much Bergoglio did to protect many persons at the time of the military dictatorship," he said.
His role after he became bishop of Buenos Aires in asking for forgiveness for the church for not having done enough at the time of the dictatorship "is also well-known," Lombardi said.
A fellow Vatican spokesman, the Rev Thomas Rosica, said the accusations "reveal left-wing elements, anti-clerical elements that are used to attack the church. They must be firmly and clearly denied."
The Vatican has a lot of experience in dealing with negative publicity campaigns against individuals or the church, he said.
As for Francis, he said, "We have information before us that gives us every assurance of the tremendous credibility of this person."
Nonetheless, the incident led to rumors and allegations that Francis was complicit in the dictatorship's appalling atrocity -- that he didn't do enough to expose it and perhaps was even partly responsible for the priests' prolonged detention, said Jim Nicholson, a former U.S. ambassador to the Holy See.
Although the allegations against Francis have never been proved, they continue to haunt him, so much so that the human rights group Center for Legal and Social Studies in Argentina opposes Francis' selection as pope.
During the years of military dictatorship, up to 30,000 students, labor leaders, intellectuals and leftists disappeared or were held in secret jails and torture centers.
The claims against the new pope have cast a shadow over what has otherwise been widely viewed as a positive start for the new pontiff, who has embraced humility and simplicity.
As pope, he will have other tough questions to deal with. He takes the helm of a Roman Catholic Church that has been rocked in recent years by sex abuse by priests, and claims of corruption and infighting among the church hierarchy.
After the pomp and activities surrounding his election as pontiff, Francis' only public engagement Friday was a meeting with all the Catholic cardinals, who wait to see what changes he will make.
Francis expressed his gratitude to Benedict XVI, saying that during his nearly eight years as pontiff, he had "reinvigorated the church with his goodness, faith, knowledge and humility."
He had words of encouragement for the cardinals, too, as they seek to take the church forward. "Go back to your homes and continue your ministry enriched by the experience of these days," he said. "Let us never give in to pessimism, to that bitterness that the devil offers us every day."
Friday's gathering, aired on Vatican TV, gave the new pontiff a chance to catch up with the cardinals who were not eligible to vote in the conclave -- those age 80 or older. That's nearly half of all cardinals.
Remarking on the fact that many are getting on in years, he said the cardinals should pass on their experience to younger generations. "Wisdom is like a good bottle of wine, and we must give it to the young people," he said.
The pope, dressed simply in white, then exchanged a few warm words with each cardinal as they left the hall one by one.
Come Tuesday, St. Peter's Square will again bustle with the faithful, tourists and locals during the official Mass to inaugurate Francis as the bishop of Rome.
The choice of day to anoint him as the holy father of the Roman Catholic Church carries a rich symbolism: It is the day that Catholics celebrate the Feast of St. Joseph to honor Jesus' father on Earth, the carpenter Joseph. It also happens to be Father's Day in Italy.
Foreign dignitaries and heads of state are welcome to attend but by tradition don't receive a specific invitation, Lombardi said.
U.S. Vice President Joe Biden is to lead the U.S. presidential delegation for the Mass, the White House said Friday, with House Democratic Leader Nancy Pelosi also among the party. On Friday, House Speaker John Boehner, a Republican, said he will send a separate bipartisan congressional delegation.
On Saturday, Francis will give an audience to the media. He will probably hold Mass on Sunday, then deliver the traditional Angelus, one of the most common Catholic prayers, the spokesman said.
Palm Sunday is just a week later, and the new pontiff will be busy, as it is the holiday that kicks off Holy Week, which culminates in Easter celebrations.
A new direction
Rosica, the Vatican spokesman, said that Francis was making his own mark as the 266th pope -- and shaking things up a little.
As head of the church, the Argentine is following the same path he took during his years as archbishop in Buenos Aires, he told CNN.
"He was a pastor there, very close to the people, and he's continued that -- he's simply changed the color of his robes right now, and the world is paying attention to every move, every word, every gesture," Rosica said.
"Those of us who were used to him in Buenos Aires are not at all surprised with this, but I can tell you that it does send some jolts through the system here, which is so deeply rooted in tradition and beautiful ceremonies and following the Book.
"Pope Francis is telling us that the Book is very important, but there's even something more important: Be faithful, be close to the people, smile and take things as they come."
Lombardi, in the news briefing, gave a similar message. "We are all learning how to behave around the holy father. We don't have instructions yet from him on how he wants to be treated," he said.
Rosica said the media's focus on the scandals surrounding the church missed the point of why Francis was elected as pope.
"The cardinals chose someone who is a model of holiness, they chose someone who has a real passion for evangelization ... which is more than just a buzzword, this is what the church is all about.
"They chose someone who has an extraordinary record for compassion, for relating to people not just within the Catholic Church ... but those on the fringes, the poor, the destitute, the disenfranchised, those living in irregular relationships, those who have suffered, those who have brought suffering upon themselves."
'Put faith first'
Francis set the tone for his vision of the church's future in his first Mass as pope Thursday, held in the Sistine Chapel with the cardinals who participated in the conclave.
With solemnity, he delivered a short, unscripted homily about moving the Catholic Church forward, saying its leaders must put faith at the heart of what they do -- or risk it becoming nothing more than a charity.
"We can walk as much as we want, we can build many things, but if we do not profess Jesus Christ, things go wrong. We may become a charitable NGO, but not the church, the bride of the Lord," he said.
"When we are not walking, we stop moving. When we are not building on the stones, what happens? The same thing that happens to children on the beach when they build sandcastles: Everything is swept away, there is no solidity."
After the Mass, the seals were ceremonially removed from the doors of the papal apartment at the Vatican, although renovation work must be done before Francis moves in. The apartment was sealed after Benedict XVI's departure two weeks ago.
Pope of firsts
When Jorge Bergoglio stepped onto the balcony at the Vatican on Wednesday evening to reveal himself as the new leader of the world's 1.2 billion Catholics, he made history as the first non-European pope of the modern era, the first from Latin America, the first Jesuit and the first to assume the name Francis.
He takes charge of a global flock at a time when confidence in the church has been dented by revelations of sex scandals and corruption claims.
A group representing the alleged victims of sexual abuse by priests wrote an open letter Francis on Thursday, requesting a meeting.
Before the conclave, the Survivors Network of those Abused by Priests (SNAP) had published a list of potential pontiffs who they felt might sweep their concerns under the rug, as well as a list of candidates they believed would lend an open ear to their concerns. Pope Francis was on neither list.
The 76-year-old is the first pope to take the name Francis. He does so in honor of St. Francis of Assisi, revered among Catholics for his work with the poor.
As pope, he brings together the first and the developing worlds. Latin America is home to 480 million Catholics -- around 40% of all those in the world.
The pontiff is seen as a conservative in doctrinal matters, as was his predecessor. As a cardinal, he clashed with the government of Argentine President Cristina Fernandez de Kirchner over his opposition to gay marriage and free distribution of contraceptives.
However, Francis' first public appearance as pope -- when he appealed for the crowds to pray for him before he gave a blessing -- suggested a "different pastoral style" from that of Benedict, who took a more academic approach, said Lombardi, the Vatican spokesman.
Also, on the ride back from the Sistine Chapel to the Santa Marta residence, he declined the papal car that had been prepared for him and instead took the bus with other cardinals, Lombardi said.
In Buenos Aires, Francis chose to live in an apartment rather than the archbishop's palace, passed on a chauffeured limousine, took the bus to work and cooked his own meals.
As a Jesuit, Francis is a member of the Society of Jesus, one of the biggest and most important orders in the church.
Jesuits are recognized for their exceptional educational institutions and focus on social justice. They have a reputation for avoiding positions of power.
CNN's Hada Messia reported from Vatican City, Laura Smith-Spark wrote and reported in London. Mariano Castillo, Ben Brumfield and Ed Payne contributed in Atlanta.