Brazil and Mexico have both summoned the American ambassadors over allegations that the US government spied on those country's presidents.
Both countries demanded the US investigate and explain whether its National Security Agency had illegally monitored communications by Brazil's President Dilma Rousseff and her Mexican counterpart, Enrique Peña Nieto.
Internet data from the two leaders was intercepted, journalist Glenn Greenwald told Brazil's TV Globo.
Mr Greenwald obtained secret files from US whistle-blower Edward Snowden.
Brazil said data interception would represent an unacceptable violation of sovereignty. Mexico called for a probe, the BBC reports.
Mexico requested an "an exhaustive investigation" to determine who may be responsible for the alleged spying on Mr Pena Nieto's emails before his election last year.
In July, Brazilian newspaper O Globo reported that the US had seized web traffic and phone calls across the region.
Mr Greenwald, a columnist for the British Guardian newspaper, told TV Globo secret documents leaked by Mr Snowden showed how US agents had spied on communications between aides of Ms Rousseff.
Brazil's Justice Minister Jose Eduardo Cardozo said that "if these facts prove to be true, it would be unacceptable and could be called an attack on our country's sovereignty".
According to the report, the NSA also used a programme to access all internet content that Ms Rousseff visited online.
The BBC's correspondent in Sao Paulo says there is a suspicion in Brazil that the US is spying on its government's communications because of commercial interests.
The revelations come at sensitive moment for Ms Rousseff, who due to make her first state visit to the United States in October.