The probe comes amid European outrage over revelations that the United States snooped on the telephone and online communications of millions of ordinary citizens in Europe, and on allied world leaders like German Chancellor Angela Merkel.
The Spanish probe will aim to establish if there are signs that a criminal offence took place, if there is anyone who could be held accountable and if Spanish courts are competent to investigate, a spokesman for the public prosecutor's office said.
Spain's El Mundo newspaper on Monday published a classified document purportedly showing that the US security services tracked 60.5 million Spanish telephone calls in a single month as part of a worldwide espionage programme that has enraged Europe.
The National Security Agency recorded the origin and destination of the calls and their duration but not the content, said El Mundo, which printed a classified graph showing 30 days of call tracing up to January 8th this year.
The article was jointly authored by US blogger Glenn Greenwald, who said he had access to previously secret documents obtained by former US intelligence contractor Edward Snowden.
El Mundo urged Spanish prosecutors to charge the NSA with spying, saying such tracing of telephone calls without the proper judicial authority amounted to a criminal offence.
Spanish Foreign Minister Jose Manuel Garcia Margallo said that if the reported espionage was confirmed "it could mean a break in the climate of trust that has traditionally reigned in relations between the two countries".
Spain summoned the US ambassador Monday to the foreign ministry to discuss the spying allegations and called on Washington to provide "all necessary information" about the alleged phone tapping.
Also on Tuesday, Spain's left-wing Izquiera Unida party called on the head of Spain's CNI intelligence agency, Félix Sanz Roldán, to appear in parliament to provide information held by the government on US espionage in Spain.