The NSA monitored communications of the leaders of Brazil and Mexico, Guardian journalist Glenn Greenwald said in an interview on Brazilian television, according to the Associated Press.
The revelations come days before President Obama is to travel to Russia for a meeting of the G20.
National Security Agency leaker Edward Snowden has leaked thousands of documents related to the U.S. surveillance programs to Greenwald.
The document from June 2012 shows who Nieto was considering for appointments to key government posts, according to the AP report.
While Greenwald said that document shows “specific intercepted messages” in the case of Nieto, the tracking of Brazilian President Dilma Rousseff was done through a program known as DNI Presenter that allows the NSA to open and read emails and online chats, the AP report said.
It said the U.S. targeting mapped out the aides with whom Rousseff communicated and tracked patterns of how those aides communicated with one another.
The NSA programs seem likely to come up in some of Obama’s meetings at the G20 in St. Petersburg. Brazil and Mexico are both members of the G20, and Snowden has been granted asylum by Russia.