VATICAN CITY: Pope Francis' diplomatic skills were put to the test Monday as he lunched with Argentine President Cristina Fernandez: As leader of Argentina's Catholics, he had accused her government of demagoguery while she called his position on gay adoptions reminiscent of the Middle Ages and the Inquisition.

That was then. On Monday, Fernandez gave the new pope a mate gourd and straw, to hold the traditional Argentine tea that Francis loves, and he gave her a kiss.

"Never in my life has a pope kissed me!" Fernandez said afterwards.

Fernandez called on the former Archbishop of Buenos Aires at his temporary home, the Vatican hotel on the edge of the Vatican gardens, and 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 1 million people to Rome.

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. Argentina in 2010 became the first Latin American country to legalize same-sex marriages.

According to Francis' 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" and saying 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 even 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.

The Fernandez meeting isn't the only diplomatic dance Francis will be conducting this week as more than 132 government 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 1 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.

One significant VIP is the spiritual leader of the world's Orthodox Christians, Ecumenical Patriarch Bartholomew I. His presence at the installation is the first from the Istanbul-based Patriarchate in nearly 1,000 years since the Great Schism divided the church in 1054.

The Mass will make several gestures toward Eastern rite and Orthodox Christians, with the Gospel being chanted in Greek as opposed to Latin and eastern rite Catholic prelates joining Francis at an initial prayer at the tomb of St. Peter under the basilica's main altar, the Vatican said Monday.

In all, some 33 Christian delegations will be present, as well as representatives of Jewish, Muslim, Buddhist, Sikh and Jain communities. They will see a simplified Mass compared to the 2005 installation of Pope Benedict XVI, with for example fewer cardinals pledging obedience to the new pope.

Also arriving in Rome on Monday was Taiwanese President Ma Ying-jeou, a rare European foray for the head of the diplomatically isolated island that underscores the tricky nature of its relations with China and the Vatican.

"We want to have much better relations with the Vatican and I think we will, thank you," Ma said as he arrived. He said Francis was a "wonderful person. I think he'll do a very good job."

Taiwan has full diplomatic relations with only 23 countries, most of them in Latin America, Africa, and the south Pacific. Its only diplomatic ally in Europe is the Vatican, though even that tie remains tenuous.

The Vatican has long expressed a willingness to transfer its diplomatic recognition from Taipei to Beijing, though it has made that conditional on China allowing its Catholics to worship freely, without Communist Party restrictions.

China has congratulated the new pope on his election, but said that establishing formal relations would depend on the Vatican cutting ties with Taipei and ceasing activities Beijing considers interference in its internal affairs.

State radio in Zimbabwe said Monday that President Robert Mugabe had also arrived in Rome for the inaugural Mass.

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.