Cardinal Jorge Bergoglio's election as the new pope was received with shock in his native Argentina - where the media highlighted his "frosty" relationship with President Cristina Fernandez de Kirchner.
Hundreds congregated at the Cathedral of Buenos Aires to celebrate the nomination of Francis, Latin America's first pontiff.
The news caught representatives at the country's Chamber of Deputies in full session and paying homage to the recently deceased president Hugo Chavez of Venezuela.
Clarin newspaper reported on its website that deputies aligned with Ms Fernandez refused to interrupt the tribute to Mr Chavez despite heated protests from the opposition.
About an hour and a half after the announcement that the Archbishop of Buenos Aires had been made Pope Francis, Ms Fernandez tweeted a congratulatory letter.
Addressing the new pope, she said: "In my name, that of the Argentine government and representing the people of our country, I want to salute you on the occasion of your election as the Roman Pontiff of the Universal Church.
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"It is our desire that, as you undertake the leadership and guidance of the Church, you should have a fruitful pastoral work carrying out such great responsibilities in pursuit of justice, equality, fraternity and the peace of humankind.
"I forward to your Holiness my esteem and respect."
Despite the warm words, the country's media was quick to point out that the new pope had a history of confrontation with Ms Fernandez and her predecessor as President and husband, the late Nestor Kirchner.
The main point of friction with Argentina's current ruler has been same-sex marriage, which Ms Fernandez's government legalised in July 2010.
Commenting on the matter at the time, Cardinal Bergoglio said: "Let us not be naive - this is not simply a political struggle, it is the aspiration to destroy God's plan."
For his part, Mr Kirchner went so far as to describe Bergoglio as the "real representative of the opposition" during his time in power, while the Church was critical with the President's "strident" style.
In a snipe at Bergoglio, Mr Kirchner reportedly said: "Our God is everyone's, but careful because the Devil also reaches everyone - those who wear trousers and those who wear cassocks."
Despite their differences, Bergoglio called for the Argentine people to pray for Mr Kirchner when he died in October 2010.