Argentine President Cristina Kirchner on Monday asked compatriot Pope Francis to mediate in the Falkland Islands' dispute with Britain at the new pontiff's first talks with a head of state, as world leaders flew in for his inauguration mass.
"I asked his intervention to promote dialogue between the two sides," Kirchner told reporters after meeting Latin America's first pope in the Vatican, warning against a growing "militarisation" in the South Atlantic.
Kirchner noted that pope John Paul II had mediated in a similar dispute between Argentina and Chile -- when the two countries nearly went to war over the islands of the Beagle channel in 1978.
Argentine media have quoted Francis, former archbishop of Buenos Aires Jorge Bergoglio, as telling reporters in 2011 that the Falklands, known as the Malvinas in Argentina, are "ours".
British Prime Minister David Cameron said Friday that he "respectfully" disagreed with those comments. In a referendum this month, 99.8 percent of the Falkland islands' inhabitants voted to remain British.
The sparsely populated archipelago triggered a war between Britain and Argentina in 1982.
"We have a very different historic opportunity now, much more favourable. In both countries, Britain and Argentina, there are democracies," Kirchner said.
The new pope when he was archbishop of Buenos Aires had testy relations with Kirchner in Argentina, particularly over legislation on gay marriage, abortion and transsexual identity.
Kirchner's late husband Nestor had called him "the true head of the opposition" because of his behind-the-scenes meetings with political leaders.
The Argentine pope -- the first non-European pontiff in nearly 1,300 years -- is also still haunted by criticism from leftists in Argentina for failing to speak out during the military era's "Dirty War" (1976-1983) when he was head of the country's Jesuits.
The Vatican has firmly denied claims that he failed to protect two Jesuit priests who were tortured by the regime, saying that he had in fact protected lives during the dictatorship.
The controversy has failed to dampen enthusiasm in Rome after a disarmingly informal style that is unusual in the Vatican and some bold statements by Francis in the early days of his papacy.
He has called for a "poor Church for the poor", has warned cardinals against worldly glories and has said the Church could crumble away "like a sand castle" without spiritual renewal.
The leader of the world's 1.2 billion Roman Catholics will be formally inaugurated Tuesday at a mass in St Peter's Square, with the Vatican saying hundreds of thousands of people are expected.
Francis will receive the papal pallium -- a strip of wool worn over the shoulders -- and the traditional "Fisherman's Ring" bearing an image of St Peter, the first pope.
In what is being seen as another sign of the new pope's more modest tastes, the ring will be gold-plated silver instead of the pure gold usually used for this emblem of papal power.
The mass begins at 0830 GMT and will be preceded by a tour of the square by the pope. It will be co-celebrated by scores of senior Church figures as well as prelates from the Eastern Catholic Churches.
The mass coincides with the feast day of St Joseph, patron saint of the universal Church, an important date in the Christian calendar.
-- 'Reaching out to poor, dispossessed' --
Vatican spokesman Federico Lombardi said 132 foreign delegations will attend, including 31 presidents, 11 heads of government and six kings and queens.
A particularly controversial visitor is Zimbabwean President Robert Mugabe, a practising Catholic, who is widely criticised for human rights abuses. He flew into Rome on Monday, sidestepping a travel ban that applies to the European Union but not to the sovereign Vatican City state.
The new pope also faces a diplomatic minefield with the planned attendance of Taiwanese President Ma Ying-jeou, which sparked an angry response from Beijing.
China, which bitterly opposes any steps that imply recognition of Taiwan by other countries, has long had strained relations with the Vatican in a dispute about authority over Catholics in the country.
"No one is privileged, no one is refused, everyone is welcome if they say they are coming," Lombardi said, stressing that the Vatican did not send out specific invites for such events.
US Vice President Joe Biden, also a practising Catholic, arrived late Sunday. At a meeting with Italian President Giorgio Napolitano, Biden quipped: "I didn't realise you'd arrange for a new pope so quickly... They're quicker than American politics!"
He continued: "I'm delighted to be here for Pope Francis. He shares a vision that all of us share, to reach out to the poor and the dispossessed."
Francis was the surprise choice in a conclave of cardinals in the Sistine Chapel last week to replace Benedict XVI, who resigned last month aged 85 saying he was getting too old for the job.
As expected, Francis is attracting a heavyweight turnout from Latin America, home to two in five of the world's Catholics, although he has urged his compatriots to save their money and make donations to the poor instead of travelling.
Brazilian President Dilma Rousseff, a former leftist guerrilla fighter, has arrived in Rome and Mexican President Enrique Pena Nieto is expected.
Chilean President Sebastian Pinera was also in Rome and tweeted that it was a "very emotional" time.