The emails of Mexican President Enrique Peno Neito (pictured above) were accessed at least a month before being elected, journalist Glenn Greenwald told Globo's news program "Fantastico" late Sunday.

Greenwald, who has reported extensively on documents provided by former NSA contractor Edward Snowden, cited a June 2012 document showing that emails were scanned to determine who Peno Nieto might name to minister posts.

A separate document showed that communications patterns between Brazilian President Dilma Rousseff and her top aids were monitored, though no specific messages were included in the report.

That document "doesn't include any of Dilma's specific intercepted messages, the way it does for Nieto," Greenwald told the Associated Press news agency in an email.

"But it is clear in several ways that her communications were intercepted, including the use of DNI Presenter, which is a program used by NSA to open and read emails and online chats."

The program allows NSA agents to access the entire communications network of the president and her staff, including telephone, Internet and social network data. Fantastico said both documents were part of an NSA case study demonstrating how data could be "intelligently" filtered.

Rousseff is due to travel to the US in October for an official state visit intended to demonstrate strengthened relations between her country and Washington.

On Monday, the US Ambassador to Brazil, Thomas Shannon, was summoned by authorities to explain the spying claims made in the Fantastico report.

The Mexican foreign ministry said it sent a diplomatic note to Washington calling for an "exhaustive investigation" into the spying claims. The country warned that if the claims are proven true, they would be a "violation of international rights."

'Violation' of sovereignty

Brazil's Justice Minister Eduardo Cardozo told the O Globo newspaper 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 US and Brazil have," he said.

In July, Greenwald worked with O Globo to publish documents revealing that the US had established a joint CIA-NSA base in Brazil to collect data on billions of emails and calls flowing through the country.

Last week, Cardozo met with US Vice President Joe Biden and other officials to discuss the details of that disclosure, which were denounced by the Brazilian government.

Snowden, a former NSA contractor, is now a fugitive in Russia under temporary asylum. He is wanted by Washington on espionage charges linked to media disclosures about US surveillance programs.

dr/ipj (AP, Reuters, AFP)