Mexico has condemned alleged spying by the US following a report by a German newspaper that said the NSA accessed its former President's emails.
Der Speigel reported that data leaked by NSA whistle-blower Edward Snowden showed that ex-President Felipe Calderon's emails were illegally accessed in 2010.
According to the report, operation "Flatliquid" saw the NSA hack a mail server used by the President an cabinet members for diplomatic and economic communications.
The NSA's Tailored Access Operations (TAO) unit "successfully exploited a key mail server" in the Mexican Presidencia domain within the Mexican Presidential network. This allowed the agency to gain access to President Felipe Calderon's public email account.
The hack unearthed information about diplomatic and economic matters, including details about Mexico's ongoing war against drug cartels that are rife in the country.
Mexico's foreign ministry said that this "practice is unacceptable, unlawful and is contrary to Mexican law and international law."
"In a relationship between neighbours and partners, there's no room for the practices that allegedly took place," the foreign ministry said in a statement.
Relations between the two countries have been tense since it was revealed by Brazilian TV station Globo in September that the NSA had also monitored others including then-presidential candidate Enrique Pea Nieto an last summer. Pea Nieto, who is the current Mexican President, has summoned the US ambassador to Mexico to demand an investigation into the issue.
Mexico has shown more restraint in its dealings with its next-door neighbour than Brazil, which has also been subject to snooping by the NSA. Its President Dilma Rousseff called off a state visit to the US following revelations that the NSA had also been accessing her communications.
