El Mundo said the bar graph document titled "Spain - Last 30 days" showed daily call traffic volume between Dec. 10, 2012, and Jan. 8, 2013. It says the NSA monitored the numbers and duration of the calls, but not their content. The document does not show the numbers.
El Mundo said the Metadata system used by the NSA could also monitor emails and phone texts, although these were not shown on the graph.
The newspaper said the document was one those leaked by former NSA contractor Edward Snowden, who is wanted by the United States but has been granted asylum in Russia.
Just as the Le Monde report, the El Mundo story was co-written by Glenn Greenwald, who originally revealed the NSA surveillance program based on leaks from Snowden. El Mundo said it had reached a deal with Greenwald to have the exclusive on the Snowden documents relating to Spain.
U.S. Ambassador James Costos, who was summoned by Spain last week to discuss reports that Spain had been targeted, met with Foreign Ministry officials for 45 minutes Monday.
Afterward, the ministry made no direct reference to the El Mundo report but called on U.S. authorities to hand over all the necessary information concerning "supposed eavesdropping carried out in Spain."
Spain warned the United States "of the importance of preserving the climate of confidence existing in bilateral relations and to know the extent of practices, which if true, are impropriate and unacceptable between friendly allies," the ministry said in a statement.
Costos, for his part, reminded Spain how it has benefited from U.S. intelligence.
The U.S. "acknowledges that some of our closest allies have raised concerns about the recent series of unauthorized disclosures of classified information," the ambassador said.
He said the programs referred to in the media "are national security programs that have played a critical role in protecting citizens of the United States. They have also played an instrumental role in our coordination with our allies and in protecting their interests as well."
Costos referred to an internal review ordered by U.S. President Obama to ensure that the intelligence that is collected is "intelligence that should and needs to be collected.
"Ultimately, the United States needs to balance the important role that these programs play in protecting our national security and protecting the security of our allies with legitimate privacy concerns," he said in his statement.
So far, Spain has insisted it is unaware of any cases of U.S. spying on Spain.
But Spain's leading newspaper El Pais last Friday cited unidentified sources that saw documents obtained by Snowden as saying they showed that the NSA had tracked phone calls, text messages and emails of millions of Spaniards and spied on members of the Spanish government and other politicians.
At a European Union summit on Friday, Merkel and French President Francois Hollande said they would press the Obama administration to agree by year's end to limits that could put an end to the alleged American eavesdropping on foreign leaders, businesses and innocent citizens.