Washington would respond through diplomatic channels to the alleged spying on Mexico by the U.S. National Security Agency (NSA), the U.S. embassy has said.
"We are not going to comment publicly on every aspect of an alleged intelligence activity," the embassy said in a statement.
Citing documents from former NSA contractor Edward Snowden, Germany's Spiegel weekly had reported that the NSA illegally accessed in 2010 the email account of then Mexican President Felipe Calderon.
According to the report, in an operation called "Flatliquid," the NSA successfully hacked into "a mail server for access to Calderon's account and the Mexican presidential domain used by cabinet members for diplomatic and economic communications."
However, the embassy said the U.S. policy on collecting intelligence data was the same as all other nations and the United States valued cooperation with all countries on matters of mutual interest.
The Mexican government on Sunday condemned the reported U.S. spying, Xinhua reported.
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"This practice is unacceptable, unlawful and is contrary to Mexican law and international law," the Mexican Foreign Ministry said in a statement released Sunday afternoon.
The ministry announced that the Mexican government would reiterate in a diplomatic note "the importance to our country of that investigation, which should be completed very soon."
"In a relationship between neighbors and partners, there's no room for the practices that allegedly took place," the foreign ministry said, reiterating its call for President Barack Obama's administration to conduct a thorough investigation into NSA conduct.
Earlier revelations from Snowden showed that the NSA also spied on Brazilian President Dilma Rousseff, and current Mexican President Enrique Pena Nieto in 2012 when he was a candidate and again as president-elect.
After the disclosure of the alleged espionage, Mexico summoned the U.S. ambassador to explain.
Nieto also discussed the issue with Obama during a private meeting held in Russia early September.