The Argentinian president has accused Britain of double standards over Crimea because London's condemnation of a referendum contradicted its support for a similar poll in the Falklands.
After a meeting with Pope Francis at the Vatican, Cristina Fernández de Kirchner said that Britain's different stance on the two votes defied logic.
"If those in Crimea hold a referendum it's bad, but if the Kelpers [Falkland Islanders] do so that's fine," Kirchner said. "It doesn't stand up to any analysis."
Crimeans, a majority of whom are ethnic Russians, voted overwhelmingly for annexation to Moscow in the wake of a revolution that toppled Kremlin-backed president Viktor Yanukovich in Kiev.
The referendum was condemned by Western powers for breaching the Ukrainian constitution and because it was held under military occupation by pro-Russian forces.
Prime minister David Cameron said the vote was "illegitimate and illegal," while foreign secretary William Hague denounced it as a "mockery of proper democratic practice".
Before signing a treaty accepting the Black Sea peninsula as part of Russia, President Vladimir Putin said Crimean authorities had called the referendum in accordance to the UN principle of self-determination.
The same principle was cited by Cameron as he welcomed the outcome of a vote by Falkland Islanders who decided to remain part of the UK last year.
"The Falkland Islands may be thousands of miles away but they are British through and through and that is how they want to stay," Cameron said. "People should know we will always be there to defend them.
"We believe in self-determination," he added.
The Falklands referendum was called by the island government on the 30th anniversary of the 74-day war between Britain and Argentina over the Atlantic archipelago.
Prior to the Crimea referendum, Russian foreign minister Sergei Lavrov had warned the West: "Crimea means more to Russia than the Falklands mean to Britain".