Argentine President Javier Milei has referred to Brazilian President Luiz Inácio Lula da Silva as a "thief" and a "convicted criminal."

Brasília has condemned the remarks as an insult to the Brazilian government, its people, and democratic institutions.

In response, a formal protest has been lodged through the Brazilian ambassador to Argentina, igniting fresh diplomatic tensions between the two nations.

During a political rally in São Paulo on Saturday, Milei spoke at the opening campaign event for right-wing presidential candidate Flávio Bolsonaro ahead of the upcoming presidential election in October.

Without explicitly naming Lula, Milei targeted him with the labels "thief" and "convicted criminal," alluding to Lula's imprisonment in corruption cases prior to 2022.

In his speech, Milei also criticized Brazilian Supreme Court Justice Alexandre de Moraes, who is overseeing ongoing legal proceedings against former President Jair Bolsonaro.

Justice de Moraes recently denied Milei permission to meet with Bolsonaro, who is currently under house arrest.

Citing AFP, an anonymous Brazilian diplomat stated that Milei's remarks were offensive to the Brazilian government, its citizens, and the country's democratic institutions.

Speaking at an event on Sunday, Lula did not mention Milei by name, but asserted that it is completely unacceptable for a foreign leader to visit Brazil and interfere in the nation's internal affairs.

According to analysts, this incident threatens to further deepen the existing diplomatic friction between Brazil and Argentina, South America's two largest economies and vital trade partners.

Lula is currently running for re-election. His primary opponent in the race is Senator Flávio Bolsonaro, whose family maintains close political ties to the political circle of former U.S. President Donald Trump.