Argentina's Economy Minister Nicolas Dujovne resigned Saturday after a week of economic tumult caused by President Mauricio Macri's defeat in a primary poll ahead of a general election.

Dujovne will be replaced by Hernan Lacunza, economy minister for Buenos Aires province, Argentine media reported. 

The country's peso ended the week having shed 20 percent of its value against the US dollar as both Fitch and S&P cut the South American country's long-term credit rating, citing increased uncertainty and a rising risk of default.

Dujovne said, in a letter posted on the website of La Nacion newspaper, he was "convinced that, under the circumstances, the [government's] management needs significant renewal in the economic arena." 

He leaves in the middle of a deepening economic crisis following last Sunday's primary elections in which market-friendly Macri was dealt a huge blow in his bid for re-election when he polled 15 points less than center-left Peronist candidate Alberto Fernandez.

The primaries serve as a bellwether for general elections in October. Dujovne's announcement marks the first change in Macri's cabinet since voters went to the polls.

Fitch, which downgraded Argentina's credit rating two notches to "CCC," said the center-right's defeat "increases risks of a break from the policy strategy of the current administration of Mauricio Macri guided by a program with the IMF."

Fernandez, now the clear favorite to unseat Macri, has questioned the reform program backed by a $56 billion rescue package from the International Monetary Fund.