The United States has become embroiled in a new row over its controversial spying programme as allies France and Mexico condemned revelations Washington tapped millions of phonecalls and hacked into leaders' emails.
French President Francois Hollande on Monday expressed his "deep disapproval" of reports of US spying in a phone call with President Barack Obama.
France's Le Monde newspaper reported that the US National Security Agency had secretly monitored 70.3 million phone communications in France over 30 days from December 10, 2012, to January 8 this year.
The allegations, the latest from leaks by former NSA contractor Edward Snowden, also marred a visit to Paris by US Secretary of State John Kerry, where he discussed moves to try to end the war in Syria.
At the same time, German weekly Der Spiegel reported the NSA had also hacked into former Mexican president Felipe Calderon's email account.
Calderon, on Twitter, described the revelations as an "affront to the institutions of the country, given that it took place when I was president".
Hollande told Obama that the alleged practices were "unacceptable between friends and allies because they infringe on the privacy of French citizens", the French leader's office said in a statement.
The allegations come on top of previous revelations by Snowden -- who has sought safety in Russia as US authorities pursue him for leaking classified information -- that the United States had a vast, secret programme called PRISM to monitor Internet users.
French prosecutors are already investigating the programme, and French Prime Minister Jean-Marc Ayrault said he was "deeply shocked" by the new revelations.
"It's incredible that an allied country like the United States at this point goes as far as spying on private communications that have no strategic justification, no justification on the basis of national defence," he told journalists.
French Foreign Minister Laurent Fabius, on a visit to Luxembourg, said US ambassador Charles Rivkin was summoned to his ministry early Monday.
"These kinds of practices between partners that harm privacy are totally unacceptable," he told reporters, adding France needed assurances that the United States was no longer monitoring its communications.
His comments were relayed to the US ambassador during the meeting, a ministry spokesman said -- the second time in less than four months that America's top representative in France has been hauled in over revelations about US snooping.
Balancing security and privacy
Kerry refused to comment on the specific accusations, but noted that Washington was reviewing its intelligence gathering operations following protests from allied governments.
He also sought to defend the US position.
"Protecting the security of our citizens in today's world is a very complicated, very challenging task... because there are lots of people out there seeking to do harm to other people," Kerry said at a press conference after meeting Arab League officials.
"Lots of countries are engaged in the activity of trying to protect their citizens in the world," he said. "Our goal is always to try to find the right balance between protecting the privacy and security of our citizens."
According to Le Monde, the spy agency automatically picked up communications from certain phone numbers in France and recorded certain text messages under a programme code-named "US-985D".
The French daily said the documents gave grounds to believe that the NSA targeted not only people suspected of being involved in terrorism but also high-profile individuals in business and politics.
Hollande's office said the French president and Obama had agreed "to work together to determine the facts and the exact scope of surveillance activities" revealed by Le Monde.
'A lucrative source'
Der Spiegel also revealed that US agents had hacked into the Mexican presidency's network, gaining access to Calderon's account.
According to the report, the NSA said this contained "diplomatic, economic and leadership communications which continue to provide insight into Mexico's political system and internal stability".
The agency reportedly said the president's office was now "a lucrative source".
Mexican authorities said they would be seeking answers from US officials "as soon as possible".
"This practice is unacceptable, illegitimate and contrary to Mexican law and international law," the foreign ministry said.
Glenn Greenwald, an American journalist now living in Brazil who has broken many of the recent stories about secret US surveillance programmes, says Washington has spied on all Latin American countries.
Speaking to a press association in Miami, Greenwald said he would report about each case in the region and warned that more spying within the United States would also be revealed.
He also said the disclosures published by Le Monde Monday had been in the hands of the French daily for some time.
This is not the first time there have been reports that France and Mexico have been targeted in relation to NSA spying allegations since information leaked by Snowden first emerged in June.
Mexico's current President Enrique Pena Nieto has already complained to Obama over reports US spies have gone through his emails.
And Der Spiegel reported last month that in 2010 the NSA monitored the internal computer network of France's diplomats and that of the foreign ministry.
But France itself has also been accused of spying. Le Monde reported in recent months that intelligence services intercepted all communications in the country, stocking telephone and computer data for years -- accusations denied by the government.