Calls to Rousseff's office and a spokeswoman were not answered. Messages sent to a spokesman for Nena Pieto weren't immediately returned. Mexico's Foreign Ministry said had no comment.
Brazilian Justice Minister Eduardo Cardozo told the newspaper O Globo that "if the facts of the report are confirmed, they would be considered very serious and would constitute a clear violation of Brazil's sovereignty."
"This is completely outside the standard of confidence expected of a strategic partnership, as the U.S. and Brazil have," he added.
In July, Greenwald co-wrote articles in O Globo that said documents leaked by Snowden indicate Brazil was the largest target in Latin America for the NSA program, which collected data on billions of emails and calls flowing through Brazil.
The Brazilian government denounced the NSA activities outlined in the earlier reports.
Greenwald reported then that the NSA collected the data through an undefined association between U.S. and Brazilian telecommunications companies. He said he could not verify which Brazilian companies were involved or if they were aware their links were being used to collect the data.
Greenwald began writing stories based on material leaked by Snowden in May, mostly for the Guardian newspaper in Britain.
Before news of the NSA program broke, the White House announced that Rousseff would be honored with a state dinner in October during a trip to the U.S., the only such full state dinner scheduled this year for a foreign leader. The move highlighted the U.S. desire to build on improved relations since Rousseff took the presidency on Jan. 1, 2011.
Rousseff's office said last week that there were no plans to scrap the state dinner because of the NSA program.
The latest revelations were sure to increase tensions, coming on the heels of last month's detention of Greenwald's domestic partner, Brazilian citizen David Miranda, who was held for nearly nine hours at London's Heathrow airport.
British authorities stopped him as he was transiting through the airport, citing their ability to do so under anti-terrorism legislation. The U.S. government was notified beforehand that Miranda was to be stopped as he returned home to Brazil after visiting Germany, where he met with Laura Poitras, a U.S. filmmaker who works with Greenwald on the NSA stories. Miranda had some of the pair's NSA documents leaked by Snowden on memory disks.
Last week, senior British national security adviser Oliver Robbins offered a sweeping view of the government concerns about those documents before Britain's High Court, saying the 58,000 classified British documents were "highly likely" to describe techniques used in counter-terrorism operations and could reveal the identities of British intelligence officers abroad.
Guardian Editor-in-Chief Alan Rusbridger dismissed the statement as containing "unsubstantiated and inaccurate claims," and questioned the danger, arguing that the government had done little to address the issue before Miranda's detention.
After Miranda's detention, Greenwald promised he was going "to write much more aggressively than before" about government snooping.
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Bradley Brooks on Twitter: www.twitter.com/bradleybrooks
