A Brazilian news report described the alleged espionage, citing Glenn Greenwald, a Brazil-based journalist who similarly obtained documents from Snowden.
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 Globo TV's Sunday night program "Fantastico." "They aren't talking about something they are planning; they are celebrating their spying successes."