The South American nation’s central bank said the rate hike from 45% was in response to ongoing currency woes and a move to counter the risk of greater impact on local inflation.
The increase came less than a day after the country appealed to the International Monetary Fund for early release of a $50bn (£38.4bn) bailout loan previously agreed with the global bank.
IMF chief Christine Lagarde said on Wednesday she had agreed to Argentinian President Mauricio Macri’s request to speed up payments of a $50bn loan in a bid to shore up Argentina’s battered economy.
In return for IMF support, the government has committed to reducing its budget deficit to 2.7% this year, from 3.9% in 2017, and to 1.3% of GDP next year.
But the bank’s backing has so far failed to bolster the currency, which has lost more than 45% of its value against the dollar since the beginning of the year.
The Argentinian peso promptly dropped more than 7% against the dollar after the request was announced, its biggest one-day decline since the currency was allowed to float three years ago.
It went on to fall another 5% in early trading on Thursday.
Analysts and investors said it was the latest in a series of communication blunders to have worsened the market downturn and damage the administration’s credibility.
Earlier, Mr Macri’s cabinet chief, Marcos Pena, was forced to deny the government was facing an economic disaster.
“We are not facing economic failure. This is a transformation, not failure. In that transformation there are difficult moments,” he said.
Speaking at the opening of the Council of the Americas business chamber in Buenos Aires, Mr Pena put the market volatility down to Argentina’s recent history.
“We are the country that has the most times violated its international contracts in the world, which has lied and cheated the rest of the time, and has shown again and again – until now – that it is not willing to seek fiscal balance and depend on its own resources,” he said.
He insisted the path taken by Mr Macri since he took office in December 2015 was one “of fiscal balance, development and growth.”
Mr Pena said the current exchange turbulence was attributable to “structural vulnerabilities” following a massive drought that affected agricultural production, the main generator of foreign currency, and a “change in the financial and commercial context in the world, notably due to tensions between the United States and China.”
He added: “There are no magic solutions, you have to go for the truth.”