SAO PAULO, Brazil (CNN) -- The U.S. National Security Agency directly targeted the communications of the presidents of Brazil and Mexico, according to a Brazilian news report likely to heighten tensions between the United States and Latin America's two biggest economies.
The report cites Glenn Greenwald, the journalist who obtained documents from NSA leaker Edward Snowden. Greenwald, who lives in Rio de Janeiro, contributed to Globo TV's Sunday night program "Fantastico."
One of the alleged NSA documents leaked to Greenwald dates from June 2012, a month before Mexican President Enrique Pena Nieto was elected. In it, the candidate talks about whom he would select for his Cabinet if elected.
The documents did not reference any specific communications with Brazilian President Dilma Rousseff but show the methods the NSA allegedly used to track e-mails and mobile phone communications with close advisers.
"It was very clear in the documents that they had already carried out the spying," Greenwald told "Fantastico," speaking in Portuguese. "They aren't talking about something they are planning, they are celebrating their spying successes."
In response to the report, Brazilian officials summoned U.S. Ambassador Thomas Shannon on Monday.
Brazilian Justice Minister Eduardo Cardozo told CBN radio: "If it's confirmed, it is very serious because a country cannot passively accept the violation of its sovereignty."
"Any country that has its sovereignty violated has to react, take a position and use international law to put things in their place," he added. "And that's what Brazil will do."
Cardozo and Brazil's newly appointed foreign minister scheduled a press conference for Monday afternoon.
A spokesman for Mexican President Enrique Peña Nieto declined to comment Monday morning.
Mexican lawmakers stressed that the Brazilian news report had not been confirmed but demanded further explanation from the U.S. government.
"This new revelation is extremely delicate because any kind of espionage is an irregular situation that is against the law. However, we have to be clear that this is speculation. This is a leak, and it must be treated like one," said Sen. Marcela Guerra.
Guerra, a member of the ruling Institutional Revolutionary Party and president of the Senate's North American foreign relations committee, said Mexico's foreign minister should meet with the U.S. ambassador to Mexico over the matter.
"There is a feeling of deep indignation," even though the report hasn't been proven, said Rep. Fernando Zarate, secretary of the Mexican house of representatives' foreign relations committee.
"If true, it seriously violates national sovereignty," said Zarate, of the Democratic Revolution Party. "How is it possible that the telephone of a president is being monitored? What could an ordinary citizen in our country expect?"
There also was no immediate reaction from the White House.
In Brazil, bilateral relations were already strained by reports that the South American nation was one of the countries that had been most-targeted by the NSA spying program.
Rousseff is scheduled to visit U.S. President Barrack Obama in Washington in October.
Obama visited Mexico in May, stressing the importance of strengthening educational and economic ties between the two nations.
Journalist Nick Parker and CNNMexico.com's Mauricio Torres contributed to this report.