Spain on Monday met US Ambassador James Costos, summoned to explain the latest revelations in a growing scandal over the US snooping on telephone and online communications of ordinary citizens and world leaders, including German Chancellor Angela Merkel.
The news emerged as a European Parliament delegation was to begin a three-day mission to Washington to probe the impact of the surveillance on EU citizens' "fundamental rights" and discuss suspending an EU-US agreement on the transfer of bank data in the wake of the scandal.
Spanish foreign ministry officials met Costos hours after daily newspaper El Mundo published a classified document apparently showing that US security services tracked 60.5 million Spanish telephone calls in a single month.
The systematic trawling of huge volumes of digital information — or metadata — would include intercepting personal details through internet web browsers, emails, and social networks such as Facebook and Twitter, the newspaper said.
Spain's foreign ministry said it has underscored to the US ambassador its concern.
"Spain conveyed to the United States the importance of preserving the climate of trust that governs bilateral relations and of knowing the scale of practices that, if true, are inappropriate and unacceptable between countries that are partners and friends," it said in a statement.
In a separate statement, Costos said that some of the security programs play a "critical role" in protecting Americans, and are also instrumental in protecting allied interests.
He promised to work diplomatically to address Spain's concerns.
Prime Minister Mariano Rajoy said after a summit with fellow European Union leaders in Brussels on Friday that he has no evidence that Spain has been spied on.
At the summit, the 28 European Union leaders approved a statement that said they value the US relationship, but it has to be based on trust and confidence, especially in intelligence matters.
France and Germany are to lead efforts to reach a new understanding with Washington by the end of this year.
The Wall Street Journal said on Monday that the NSA had tapped the phones of around 35 world leaders, including close ally Merkel, who last week branded the snooping as unacceptable between friends.
President Barack Obama learned of the espionage program only after an internal mid-year review, and the White House then ordered an end to the spying on some leaders, including Merkel, The Wall Street Journal said.