The photo, taken at his weekly general audience in the Vatican, gained widespread attention in the South American press and was later tweeted, without additional comment, by Argentinian President Cristina Kirchner.
It was not clear whether the pontiff deliberately picked up the sign, reading in Spanish: "It's time for dialogue between Argentina and the United Kingdom on the Falklands," or whether it was thrust into his hands.
Argentina and Britain fought a war over the disputed South Atlantic archipelago in 1982, ending with Argentina's surrender after the death of 649 Argentines and 255 British troops.
London has ignored a UN resolution urging dialogue over islands.
In 2013, Kirchner asked Francis, who is Argentinian, to intervene to promote a dialogue between the countries.
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