Pope Francis's diplomatic skills were put to the test Monday as he met with Argentine President Cristina Fernandez, with whom he has clashed over her socially liberal policies and what he has called the government's totalitarianism.

Fernandez called on the former Archbishop of Buenos Aires Monday at his temporary home, the Vatican hotel on the edge of the Vatican gardens. The two later lunched together, a day before she and other world leaders attend his installation mass in St. Peter's Square that some estimates say could bring one million people to Rome.

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Pope Francis has urged fellow Argentines not to spend the money to fly to Rome for the ceremony, but to donate the funds to charity instead.

Fernandez said she has asked Pope Francis to help defuse the long-running dispute between Argentina and Britain over the Falkland Islands.

Fernandez told journalists after the meeting that she has asked for his intercession to "facilitate dialogue" over the islands, which Argentina claims and calls the Malvinas.

Just last week, British Prime Minister David Cameron said he doesn't agree with Francis's views on the Falklands. When Francis was archbishop of Buenos Aires, he had been quoted as saying that Britain "usurped" the remote islands.

Argentina and Britain fought a 1982 war over the islands. Earlier this month, the islanders voted overwhelmingly to remain a British Overseas Territory.

It was not immediately known how Francis responded to Fernandez's request.

Clashed over policies, teachings

The venue for their meeting is unusual, given the pope has technically taken possession of the papal apartment in the Apostolic Palace, where such formal audiences are usually held. For a pope who has already come to be known for his gestures, the choice was perhaps significant, though he has conducted all of his audiences in the hotel to date, including with the Vatican secretary of state earlier in the day.

The Vatican said it planned no statement, describing the meeting as private and informal.

Fernandez and her predecessor and late husband, Nestor Kirchner, defied church teaching to push through a series of measures with popular backing in Argentina, including mandatory sex education in schools, free distribution of contraceptives in public hospitals and the right for transsexuals to change their official identities on demand. In 2010, Argentina became the first Latin American country to legalize same-sex marriages.

Argentine President Cristina Fernandez de Kirchner, left, meets then Argentine Cardinal Jorge Bergoglio, now Pope Francis, Dec. 2008. Fernandez and Francis have regularly clashed over her policies and his religious teachings. (Ezequiel Pontoriero/DyN/Reuters)

According to Francis's authorized biographer, Sergio Rubin, the former Cardinal Jorge Mario Bergoglio was politically wise enough to know the church couldn't win a straight-on fight against gay marriage, so he urged his bishops to lobby for gay civil unions instead. It wasn't until his proposal was shot down by the bishops' conference that he declared what gay activists called a "war of God" on the measure — and the church lost the issue altogether.

Fernandez issued a perfunctory message of congratulations when Francis was elected last week, calling the election of the first Latin American pope "historic." She said she hoped that given his namesake, St. Francis of Assisi, the new pope would inspire world leaders to pay greater attention to the poor and pursue dialogue rather than force to resolve disputes.

She has, however, remained unusually silent about the election on her otherwise prolifically active Twitter account, posting a single tweet on his election day: "To your Holiness Francis I" with a link to her letter of congratulations, which wasn't signed.

Their chilly relations became crystal clear after the Kirchners several years ago stopped attending the church's annual "Te Deum" address challenging society to do better, which is delivered each May 25.

In last year's address, Bergoglio said Argentina was being harmed by demagoguery, totalitarianism, corruption and efforts to secure unlimited power: a strong message in a country whose president has ruled by decree and left scandals unpunished.

120 official delegations expected

The Fernandez meeting isn't the only diplomatic dance Francis will be conducting this week as more than 120 official delegations descend on Rome for the mass formally installing Francis as the 266th leader of the 1.2-billion strong Catholic Church.

Italian media say Rome civil protection authorities are planning for upward of one million people to attend the mass, numbers not seen since the beatification of Pope John Paul II in 2011 which drew 1.5 million to St. Peter's and the surrounding streets.

Canada's Governor General David Johnston, who will represent Canada at Tuesday's ceremony, has already arrived in Rome.

The ceremony will begin when Pope Francis leaves his residence at 8:50 a.m. local time (3:50 a.m. ET), Vatican spokespeople revealed at a Monday press conference.

He will make his way to the basilica where the mass will be held, but it is unclear what method of transportation he will use. Some are anticipating the Pope — who is known for his humility and desire for a simple lifestyle — will walk among the one million people crowding outside the basilica.

Inside the basilica, visiting dignitaries will be seated on one side, while religious leaders will be seated on the other.

U.S. Vice-President Joe Biden, a Roman Catholic, will be attending Francis's inauguration. Other notables include:

• A leader of the world's Orthodox Christians Eucumenical Patriarch Bartholomew I.
• Taiwanese President Ma Ying-jeou.
• Zimbabwean President Robert Mugabe.

Mugabe, 89, is the subject of a travel ban by European nations to protest his human rights record in a decade of political and economic turmoil in his southern African nation, but it does not affect his trips to the Vatican through Italy.

Former pope Benedict XVI will not attend the mass. However, Pope Francis is expected to visit the retired pope on Friday.

The Vatican also gave information about the Ring of the Fisherman, which Francis will receive during the mass, and his papal coat of arms.

The ring that Pope Francis will put on during the mass once belonged to Pope Paul VI, and is made of gold-plated silver. Francis's papal coat of arms is based on the same simple one as he had previously, with the symbol of his Jesuit order.

With files from CBC News