Mexico's former president Felipe Calderon has described allegations that the US spied on his emails when he was in office as an "affront" to his country's institutions.
Breaking his silence since the report emerged on Sunday, Calderon said on Monday he had asked Foreign Minister Jose Antonio Meade to relay to Washington his "strongest protest for the espionage of which I was the object".
"More than personal, it is an affront to the institutions of the country, given that it took place when I was president," he wrote on Twitter.
Calderon was in power for six years until December 2012, a presidency marked by unprecedented security ties with the US to combat drug cartels.
The German weekly Der Spiegel, citing documents leaked by former National Security Agency contractor Edward Snowden, said the NSA hacked into Calderon's email account in May 2010.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
This followed a report that the US spying agency had gained access to now President Enrique Pena Nieto's emails when he was a candidate last year.
The Mexican government, which has already demanded an investigation over the allegations that Pena Nieto was spied on, said it would seek answers from US officials over the new report "as soon as possible".
"This practice is unacceptable, illegitimate and contrary to Mexican law and international law," the foreign ministry said.
