The US National Security Agency spied on more than 60 million phone calls in Spain in one month alone, according to the latest leak from former American security worker Edward Snowden.
A report of the spying in the El Mundo newspaper comes a week after reports of US mass phone surveillance in France, and the tapping of German chancellor Angela Merkel's mobile phone.
El Mundo said that a document provided by the former National Security Agency contractor Snowden shows that the NSA monitored the phone calls from December 10, 2012 until January 8, 2013 but not their content.
It said the system used by the NSA could also monitor emails and phone texts.
The El Mundo story was co-written by Glenn Greenwald, who originally revealed the NSA surveillance programme based on leaks from Snowden. El Mundo said it had reached a deal with him to have the exclusive on the Snowden documents relating to Spain.
Spanish Prime Minister Mariano Rajoy has already summoned the US ambassador to Spain for a meeting, but insisted his government was unaware of any cases of US spying on Spain. He acted after another paper, El Pais, said Snowden documents showed the NSA had tracked phone calls, text messages and emails of millions of Spaniards and spied on members of the government and other politicians.
At a European Union summit on Friday Mrs 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.
Nine European MEPs are visiting Washington to get more information on the US mass surveillance.